MITRE ATT&CK® techniques for Linux

Adversaries may attempt to dump the contents of /etc/passwd and /etc/shadow to enable offline password cracking. Most modern Linux operating systems use a combination of /etc/passwd and /etc/shadow to store user account information, including password hashes in /etc/shadow. By default, /etc/shadow is only readable by the root user.[1]

Linux stores user information such as user ID, group ID, home directory path, and login shell in /etc/passwd. A "user" on the system may belong to a person or a service. All password hashes are stored in /etc/shadow - including entries for users with no passwords and users with locked or disabled accounts.[1]

Adversaries may attempt to read or dump the /etc/passwd and /etc/shadow files on Linux systems via command line utilities such as the cat command.[2] Additionally, the Linux utility unshadow can be used to combine the two files in a format suited for password cracking utilities such as John the Ripper - for example, via the command /usr/bin/unshadow /etc/passwd /etc/shadow > /tmp/crack.password.db[3]. Since the user information stored in /etc/passwd are linked to the password hashes in /etc/shadow, an adversary would need to have access to both.

Adversaries may poison Address Resolution Protocol (ARP) caches to position themselves between the communication of two or more networked devices. This activity may be used to enable follow-on behaviors such as Network Sniffing or Transmitted Data Manipulation.

The ARP protocol is used to resolve IPv4 addresses to link layer addresses, such as a media access control (MAC) address.[1] Devices in a local network segment communicate with each other by using link layer addresses. If a networked device does not have the link layer address of a particular networked device, it may send out a broadcast ARP request to the local network to translate the IP address to a MAC address. The device with the associated IP address directly replies with its MAC address. The networked device that made the ARP request will then use as well as store that information in its ARP cache.

An adversary may passively wait for an ARP request to poison the ARP cache of the requesting device. The adversary may reply with their MAC address, thus deceiving the victim by making them believe that they are communicating with the intended networked device. For the adversary to poison the ARP cache, their reply must be faster than the one made by the legitimate IP address owner. Adversaries may also send a gratuitous ARP reply that maliciously announces the ownership of a particular IP address to all the devices in the local network segment.

The ARP protocol is stateless and does not require authentication. Therefore, devices may wrongly add or update the MAC address of the IP address in their ARP cache.[2][3]

Adversaries may use ARP cache poisoning as a means to intercept network traffic. This activity may be used to collect and/or relay data such as credentials, especially those sent over an insecure, unencrypted protocol.[2]

Adversaries may circumvent mechanisms designed to control privilege elevation to gain higher-level permissions. Most modern systems contain native elevation control mechanisms that are intended to limit privileges that a user can perform on a machine. Authorization has to be granted to specific users in order to perform tasks that can be considered of higher risk.[1][2] An adversary can perform several methods to take advantage of built-in control mechanisms in order to escalate privileges on a system.[3][4]

Adversaries may interrupt availability of system and network resources by inhibiting access to accounts utilized by legitimate users. Accounts may be deleted, locked, or manipulated (ex: changed credentials, revoked permissions for SaaS platforms such as Sharepoint) to remove access to accounts.[1] Adversaries may also subsequently log off and/or perform a System Shutdown/Reboot to set malicious changes into place.[2][3]

In Windows, Net utility, Set-LocalUser and Set-ADAccountPassword PowerShell cmdlets may be used by adversaries to modify user accounts. Accounts could also be disabled by Group Policy. In Linux, the passwd utility may be used to change passwords. On ESXi servers, accounts can be removed or modified via esxcli (`system account set`, `system account remove`).

Adversaries who use ransomware or similar attacks may first perform this and other Impact behaviors, such as Data Destruction and Defacement, in order to impede incident response/recovery before completing the Data Encrypted for Impact objective.

Adversaries may attempt to get a listing of valid accounts, usernames, or email addresses on a system or within a compromised environment. This information can help adversaries determine which accounts exist, which can aid in follow-on behavior such as brute-forcing, spear-phishing attacks, or account takeovers (e.g., Valid Accounts).

Adversaries may use several methods to enumerate accounts, including abuse of existing tools, built-in commands, and potential misconfigurations that leak account names and roles or permissions in the targeted environment.

For examples, cloud environments typically provide easily accessible interfaces to obtain user lists.[1][2] On hosts, adversaries can use default PowerShell and other command line functionality to identify accounts. Information about email addresses and accounts may also be extracted by searching an infected system’s files.

Adversaries may manipulate accounts to maintain and/or elevate access to victim systems. Account manipulation may consist of any action that preserves or modifies adversary access to a compromised account, such as modifying credentials or permission groups.[1] These actions could also include account activity designed to subvert security policies, such as performing iterative password updates to bypass password duration policies and preserve the life of compromised credentials.

In order to create or manipulate accounts, the adversary must already have sufficient permissions on systems or the domain. However, account manipulation may also lead to privilege escalation where modifications grant access to additional roles, permissions, or higher-privileged Valid Accounts.

An adversary may add additional local or domain groups to an adversary-controlled account to maintain persistent access to a system or domain.

On Windows, accounts may use the `net localgroup` and `net group` commands to add existing users to local and domain groups.[1][2] On Linux, adversaries may use the `usermod` command for the same purpose.[3]

For example, accounts may be added to the local administrators group on Windows devices to maintain elevated privileges. They may also be added to the Remote Desktop Users group, which allows them to leverage Remote Desktop Protocol to log into the endpoints in the future.[4] Adversaries may also add accounts to VPN user groups to gain future persistence on the network.[5] On Linux, accounts may be added to the sudoers group, allowing them to persistently leverage Sudo and Sudo Caching for elevated privileges.

In Windows environments, machine accounts may also be added to domain groups. This allows the local SYSTEM account to gain privileges on the domain.[6]

Adversaries may attempt to position themselves between two or more networked devices using an adversary-in-the-middle (AiTM) technique to support follow-on behaviors such as Network Sniffing, Transmitted Data Manipulation, or replay attacks (Exploitation for Credential Access). By abusing features of common networking protocols that can determine the flow of network traffic (e.g. ARP, DNS, LLMNR, etc.), adversaries may force a device to communicate through an adversary controlled system so they can collect information or perform additional actions.[1]

For example, adversaries may manipulate victim DNS settings to enable other malicious activities such as preventing/redirecting users from accessing legitimate sites and/or pushing additional malware.[2][3][4] Adversaries may also manipulate DNS and leverage their position in order to intercept user credentials, including access tokens (Steal Application Access Token) and session cookies (Steal Web Session Cookie).[5][6] Downgrade Attacks can also be used to establish an AiTM position, such as by negotiating a less secure, deprecated, or weaker version of communication protocol (SSL/TLS) or encryption algorithm.[7][8][9]

Adversaries may also leverage the AiTM position to attempt to monitor and/or modify traffic, such as in Transmitted Data Manipulation. Adversaries can setup a position similar to AiTM to prevent traffic from flowing to the appropriate destination, potentially to impair defenses and/or in support of a Network Denial of Service.

Adversaries may target resource intensive features of applications to cause a denial of service (DoS), denying availability to those applications. For example, specific features in web applications may be highly resource intensive. Repeated requests to those features may be able to exhaust system resources and deny access to the application or the server itself.[1]

Adversaries may communicate using OSI application layer protocols to avoid detection/network filtering by blending in with existing traffic. Commands to the remote system, and often the results of those commands, will be embedded within the protocol traffic between the client and server.

Adversaries may utilize many different protocols, including those used for web browsing, transferring files, electronic mail, DNS, or publishing/subscribing. For connections that occur internally within an enclave (such as those between a proxy or pivot node and other nodes), commonly used protocols are SMB, SSH, or RDP.[1]

Adversaries may attempt to get a listing of open application windows. Window listings could convey information about how the system is used.[1] For example, information about application windows could be used identify potential data to collect as well as identifying security tooling (Security Software Discovery) to evade.[2]

Adversaries typically abuse system features for this type of enumeration. For example, they may gather information through native system features such as Command and Scripting Interpreter commands and Native API functions.

Adversaries may exploit software vulnerabilities that can cause an application or system to crash and deny availability to users. [1] Some systems may automatically restart critical applications and services when crashes occur, but they can likely be re-exploited to cause a persistent denial of service (DoS) condition.

Adversaries may exploit known or zero-day vulnerabilities to crash applications and/or systems, which may also lead to dependent applications and/or systems to be in a DoS condition. Crashed or restarted applications or systems may also have other effects such as Data Destruction, Firmware Corruption, Service Stop etc. which may further cause a DoS condition and deny availability to critical information, applications and/or systems.

An adversary may compress and/or encrypt data that is collected prior to exfiltration. Compressing the data can help to obfuscate the collected data and minimize the amount of data sent over the network.[1] Encryption can be used to hide information that is being exfiltrated from detection or make exfiltration less conspicuous upon inspection by a defender.

Both compression and encryption are done prior to exfiltration, and can be performed using a utility, 3rd party library, or custom method.

An adversary may compress or encrypt data that is collected prior to exfiltration using a custom method. Adversaries may choose to use custom archival methods, such as encryption with XOR or stream ciphers implemented with no external library or utility references. Custom implementations of well-known compression algorithms have also been used.[1]

An adversary may compress or encrypt data that is collected prior to exfiltration using 3rd party libraries. Many libraries exist that can archive data, including Python rarfile [1], libzip [2], and zlib [3]. Most libraries include functionality to encrypt and/or compress data.

Some archival libraries are preinstalled on systems, such as bzip2 on macOS and Linux, and zip on Windows. Note that the libraries are different from the utilities. The libraries can be linked against when compiling, while the utilities require spawning a subshell, or a similar execution mechanism.

Adversaries may use utilities to compress and/or encrypt collected data prior to exfiltration. Many utilities include functionalities to compress, encrypt, or otherwise package data into a format that is easier/more secure to transport.

Adversaries may abuse various utilities to compress or encrypt data before exfiltration. Some third party utilities may be preinstalled, such as tar on Linux and macOS or zip on Windows systems.

On Windows, diantz or makecab may be used to package collected files into a cabinet (.cab) file. diantz may also be used to download and compress files from remote locations (i.e. Remote Data Staging).[1] xcopy on Windows can copy files and directories with a variety of options. Additionally, adversaries may use certutil to Base64 encode collected data before exfiltration.

Adversaries may use also third party utilities, such as 7-Zip, WinRAR, and WinZip, to perform similar activities.[2][3][4]

Adversaries may employ a known asymmetric encryption algorithm to conceal command and control traffic rather than relying on any inherent protections provided by a communication protocol. Asymmetric cryptography, also known as public key cryptography, uses a keypair per party: one public that can be freely distributed, and one private. Due to how the keys are generated, the sender encrypts data with the receiver’s public key and the receiver decrypts the data with their private key. This ensures that only the intended recipient can read the encrypted data. Common public key encryption algorithms include RSA and ElGamal.

For efficiency, many protocols (including SSL/TLS) use symmetric cryptography once a connection is established, but use asymmetric cryptography to establish or transmit a key. As such, these protocols are classified as Asymmetric Cryptography.

Adversaries may abuse the at utility to perform task scheduling for initial or recurring execution of malicious code. The at utility exists as an executable within Windows, Linux, and macOS for scheduling tasks at a specified time and date. Although deprecated in favor of Scheduled Task's schtasks in Windows environments, using at requires that the Task Scheduler service be running, and the user to be logged on as a member of the local Administrators group. In addition to explicitly running the `at` command, adversaries may also schedule a task with at by directly leveraging the Windows Management Instrumentation `Win32_ScheduledJob` WMI class.[1]

On Linux and macOS, at may be invoked by the superuser as well as any users added to the at.allow file. If the at.allow file does not exist, the at.deny file is checked. Every username not listed in at.deny is allowed to invoke at. If the at.deny exists and is empty, global use of at is permitted. If neither file exists (which is often the baseline) only the superuser is allowed to use at.[2]

Adversaries may use at to execute programs at system startup or on a scheduled basis for Persistence. at can also be abused to conduct remote Execution as part of Lateral Movement and/or to run a process under the context of a specified account (such as SYSTEM).

In Linux environments, adversaries may also abuse at to break out of restricted environments by using a task to spawn an interactive system shell or to run system commands. Similarly, at may also be used for Privilege Escalation if the binary is allowed to run as superuser via sudo.[3]

An adversary can leverage a computer's peripheral devices (e.g., microphones and webcams) or applications (e.g., voice and video call services) to capture audio recordings for the purpose of listening into sensitive conversations to gather information.[1]

Malware or scripts may be used to interact with the devices through an available API provided by the operating system or an application to capture audio. Audio files may be written to disk and exfiltrated later.

Once established within a system or network, an adversary may use automated techniques for collecting internal data. Methods for performing this technique could include use of a Command and Scripting Interpreter to search for and copy information fitting set criteria such as file type, location, or name at specific time intervals.

In cloud-based environments, adversaries may also use cloud APIs, data pipelines, command line interfaces, or extract, transform, and load (ETL) services to automatically collect data.[1]

This functionality could also be built into remote access tools.

This technique may incorporate use of other techniques such as File and Directory Discovery and Lateral Tool Transfer to identify and move files, as well as Cloud Service Dashboard and Cloud Storage Object Discovery to identify resources in cloud environments.

Adversaries may exfiltrate data, such as sensitive documents, through the use of automated processing after being gathered during Collection.[1]

When automated exfiltration is used, other exfiltration techniques likely apply as well to transfer the information out of the network, such as Exfiltration Over C2 Channel and Exfiltration Over Alternative Protocol.

Adversaries may attempt to get a listing of backup software or configurations that are installed on a system. Adversaries may use this information to shape follow-on behaviors, such as Data Destruction, Inhibit System Recovery, or Data Encrypted for Impact.

Commands that can be used to obtain security software information are netsh, `reg query` with Reg, `dir` with cmd, and Tasklist, but other indicators of discovery behavior may be more specific to the type of software or security system the adversary is looking for, such as Veeam, Acronis, Dropbox, or Paragon.[1]

Adversaries may leverage the network bandwidth resources of co-opted systems to complete resource-intensive tasks, which may impact system and/or hosted service availability.

Adversaries may also use malware that leverages a system's network bandwidth as part of a botnet in order to facilitate Network Denial of Service campaigns and/or to seed malicious torrents.[1] Alternatively, they may engage in proxyjacking by selling use of the victims' network bandwidth and IP address to proxyware services.[2] Finally, they may engage in internet-wide scanning in order to identify additional targets for compromise.[3]

In addition to incurring potential financial costs or availability disruptions, this technique may cause reputational damage if a victim’s bandwidth is used for illegal activities.[2]

Adversaries may use an existing, legitimate external Web service as a means for sending commands to and receiving output from a compromised system over the Web service channel. Compromised systems may leverage popular websites and social media to host command and control (C2) instructions. Those infected systems can then send the output from those commands back over that Web service channel. The return traffic may occur in a variety of ways, depending on the Web service being utilized. For example, the return traffic may take the form of the compromised system posting a comment on a forum, issuing a pull request to development project, updating a document hosted on a Web service, or by sending a Tweet.

Popular websites and social media acting as a mechanism for C2 may give a significant amount of cover due to the likelihood that hosts within a network are already communicating with them prior to a compromise. Using common services, such as those offered by Google or Twitter, makes it easier for adversaries to hide in expected noise. Web service providers commonly use SSL/TLS encryption, giving adversaries an added level of protection.

Adversaries may use binary padding to add junk data and change the on-disk representation of malware. This can be done without affecting the functionality or behavior of a binary, but can increase the size of the binary beyond what some security tools are capable of handling due to file size limitations.

Binary padding effectively changes the checksum of the file and can also be used to avoid hash-based blocklists and static anti-virus signatures.[1] The padding used is commonly generated by a function to create junk data and then appended to the end or applied to sections of malware.[2] Increasing the file size may decrease the effectiveness of certain tools and detection capabilities that are not designed or configured to scan large files. This may also reduce the likelihood of being collected for analysis. Public file scanning services, such as VirusTotal, limits the maximum size of an uploaded file to be analyzed.[3]

Adversaries may abuse bind mounts on file structures to hide their activity and artifacts from native utilities. A bind mount maps a directory or file from one location on the filesystem to another, similar to a shortcut on Windows. It’s commonly used to provide access to specific files or directories across different environments, such as inside containers or chroot environments, and requires sudo access.

Adversaries may use bind mounts to map either an empty directory or a benign `/proc` directory to a malicious process’s `/proc` directory. Using the commands `mount –o bind /proc/benign-process /proc/malicious-process` (or `mount –B`), the malicious process's `/proc` directory is overlayed with the contents of a benign process's `/proc` directory. When system utilities query process activity, such as `ps` and `top`, the kernel follows the bind mount and presents the benign directory’s contents instead of the malicious process's actual `/proc` directory. As a result, these utilities display information that appears to come from the benign process, effectively hiding the malicious process's metadata, executable, or other artifacts from detection.[1][2]

Adversaries may configure system settings to automatically execute a program during system boot or logon to maintain persistence or gain higher-level privileges on compromised systems. Operating systems may have mechanisms for automatically running a program on system boot or account logon.[1][2][3][4][5] These mechanisms may include automatically executing programs that are placed in specially designated directories or are referenced by repositories that store configuration information, such as the Windows Registry. An adversary may achieve the same goal by modifying or extending features of the kernel.

Since some boot or logon autostart programs run with higher privileges, an adversary may leverage these to elevate privileges.

Adversaries may use scripts automatically executed at boot or logon initialization to establish persistence.[1][2] Initialization scripts can be used to perform administrative functions, which may often execute other programs or send information to an internal logging server. These scripts can vary based on operating system and whether applied locally or remotely.

Adversaries may use these scripts to maintain persistence on a single system. Depending on the access configuration of the logon scripts, either local credentials or an administrator account may be necessary.

An adversary may also be able to escalate their privileges since some boot or logon initialization scripts run with higher privileges.

Adversaries may use bootkits to persist on systems. A bootkit is a malware variant that modifies the boot sectors of a hard drive, allowing malicious code to execute before a computer's operating system has loaded. Bootkits reside at a layer below the operating system and may make it difficult to perform full remediation unless an organization suspects one was used and can act accordingly.

In BIOS systems, a bootkit may modify the Master Boot Record (MBR) and/or Volume Boot Record (VBR).[1] The MBR is the section of disk that is first loaded after completing hardware initialization by the BIOS. It is the location of the boot loader. An adversary who has raw access to the boot drive may overwrite this area, diverting execution during startup from the normal boot loader to adversary code.[2]

The MBR passes control of the boot process to the VBR. Similar to the case of MBR, an adversary who has raw access to the boot drive may overwrite the VBR to divert execution during startup to adversary code.

In UEFI (Unified Extensible Firmware Interface) systems, a bootkit may instead create or modify files in the EFI system partition (ESP). The ESP is a partition on data storage used by devices containing UEFI that allows the system to boot the OS and other utilities used by the system. An adversary can use the newly created or patched files in the ESP to run malicious kernel code.[3][4]

An adversary may attempt to evade process tree-based analysis by modifying executed malware's parent process ID (PPID). If endpoint protection software leverages the “parent-child" relationship for detection, breaking this relationship could result in the adversary’s behavior not being associated with previous process tree activity. On Unix-based systems breaking this process tree is common practice for administrators to execute software using scripts and programs.[1]

On Linux systems, adversaries may execute a series of Native API calls to alter malware's process tree. For example, adversaries can execute their payload without any arguments, call the `fork()` API call twice, then have the parent process exit. This creates a grandchild process with no parent process that is immediately adopted by the `init` system process (PID 1), which successfully disconnects the execution of the adversary's payload from its previous process tree.

Another example is using the “daemon” syscall to detach from the current parent process and run in the background.[2][3]

Adversaries may abuse internet browser extensions to establish persistent access to victim systems. Browser extensions or plugins are small programs that can add functionality to and customize aspects of internet browsers. They can be installed directly via a local file or custom URL or through a browser's app store - an official online platform where users can browse, install, and manage extensions for a specific web browser. Extensions generally inherit the web browser's permissions previously granted.[1][2] Malicious extensions can be installed into a browser through malicious app store downloads masquerading as legitimate extensions, through social engineering, or by an adversary that has already compromised a system. Security can be limited on browser app stores, so it may not be difficult for malicious extensions to defeat automated scanners.[3] Depending on the browser, adversaries may also manipulate an extension's update url to install updates from an adversary-controlled server or manipulate the mobile configuration file to silently install additional extensions.

Adversaries may abuse how chromium-based browsers load extensions by modifying or replacing the Preferences and/or Secure Preferences files to silently install malicious extensions. When the browser is not running, adversaries can alter these files, ensuring the extension is loaded, granted desired permissions, and will persist in browser sessions. This method does not require user consent and extensions are silently loaded in the background from disk or from the browser's trusted store.[4] Previous to macOS 11, adversaries could silently install browser extensions via the command line using the profiles tool to install malicious .mobileconfig files. In macOS 11+, the use of the profiles tool can no longer install configuration profiles; however, .mobileconfig files can be planted and installed with user interaction.[5] Once the extension is installed, it can browse to websites in the background, steal all information that a user enters into a browser (including credentials), and be used as an installer for a RAT for persistence.[6][7][8][9]

There have also been instances of botnets using a persistent backdoor through malicious Chrome extensions for Command and Control.[10][11] Adversaries may also use browser extensions to modify browser permissions and components, privacy settings, and other security controls for Stealth.[12][13]

Adversaries may attempt to blend in with legitimate traffic by spoofing browser and system attributes like operating system, system language, platform, user-agent string, resolution, time zone, etc. The HTTP User-Agent request header is a string that lets servers and network peers identify the application, operating system, vendor, and/or version of the requesting user agent.[1]

Adversaries may gather this information through System Information Discovery or by users navigating to adversary-controlled websites, and then use that information to craft their web traffic to evade defenses.[2]

Adversaries may enumerate information about browsers to learn more about compromised environments. Data saved by browsers (such as bookmarks, accounts, and browsing history) may reveal a variety of personal information about users (e.g., banking sites, relationships/interests, social media, etc.) as well as details about internal network resources such as servers, tools/dashboards, or other related infrastructure.[1]

Browser information may also highlight additional targets after an adversary has access to valid credentials, especially Credentials In Files associated with logins cached by a browser.

Specific storage locations vary based on platform and/or application, but browser information is typically stored in local files and databases (e.g., `%APPDATA%/Google/Chrome`).[2]

Adversaries may use brute force techniques to gain access to accounts when passwords are unknown or when password hashes are obtained.[1] Without knowledge of the password for an account or set of accounts, an adversary may systematically guess the password using a repetitive or iterative mechanism.[2] Brute forcing passwords can take place via interaction with a service that will check the validity of those credentials or offline against previously acquired credential data, such as password hashes.

Brute forcing credentials may take place at various points during a breach. For example, adversaries may attempt to brute force access to Valid Accounts within a victim environment leveraging knowledge gathered from other post-compromise behaviors such as OS Credential Dumping, Account Discovery, or Password Policy Discovery. Adversaries may also combine brute forcing activity with behaviors such as External Remote Services as part of Initial Access.

If an adversary guesses the correct password but fails to login to a compromised account due to location-based conditional access policies, they may change their infrastructure until they match the victim’s location and therefore bypass those policies.[3]

Adversaries may attempt to access cached domain credentials used to allow authentication to occur in the event a domain controller is unavailable.[1]

On Windows Vista and newer, the hash format is DCC2 (Domain Cached Credentials version 2) hash, also known as MS-Cache v2 hash.[2] The number of default cached credentials varies and can be altered per system. This hash does not allow pass-the-hash style attacks, and instead requires Password Cracking to recover the plaintext password.[3]

On Linux systems, Active Directory credentials can be accessed through caches maintained by software like System Security Services Daemon (SSSD) or Quest Authentication Services (formerly VAS). Cached credential hashes are typically located at `/var/lib/sss/db/cache.[domain].ldb` for SSSD or `/var/opt/quest/vas/authcache/vas_auth.vdb` for Quest. Adversaries can use utilities, such as `tdbdump`, on these database files to dump the cached hashes and use Password Cracking to obtain the plaintext password.[4]

With SYSTEM or sudo access, the tools/utilities such as Mimikatz, Reg, and secretsdump.py for Windows or Linikatz for Linux can be used to extract the cached credentials.[4]

Note: Cached credentials for Windows Vista are derived using PBKDF2.[2]

Adversaries may attempt to steal Kerberos tickets stored in credential cache files (or ccache). These files are used for short term storage of a user's active session credentials. The ccache file is created upon user authentication and allows for access to multiple services without the user having to re-enter credentials.

The /etc/krb5.conf configuration file and the KRB5CCNAME environment variable are used to set the storage location for ccache entries. On Linux, credentials are typically stored in the `/tmp` directory with a naming format of `krb5cc_%UID%` or `krb5.ccache`. On macOS, ccache entries are stored by default in memory with an `API:{uuid}` naming scheme. Typically, users interact with ticket storage using kinit, which obtains a Ticket-Granting-Ticket (TGT) for the principal; klist, which lists obtained tickets currently held in the credentials cache; and other built-in binaries.[1][2]

Adversaries can collect tickets from ccache files stored on disk and authenticate as the current user without their password to perform Pass the Ticket attacks. Adversaries can also use these tickets to impersonate legitimate users with elevated privileges to perform Privilege Escalation. Tools like Kekeo can also be used by adversaries to convert ccache files to Windows format for further Lateral Movement. On macOS, adversaries may use open-source tools or the Kerberos framework to interact with ccache files and extract TGTs or Service Tickets via lower-level APIs.[3][4][5][6]

In addition to clearing system logs, an adversary may clear the command history of a compromised account to conceal the actions undertaken during an intrusion. Various command interpreters keep track of the commands users type in their terminal so that users can retrace what they've done.

On Linux and macOS, these command histories can be accessed in a few different ways. While logged in, this command history is tracked in a file pointed to by the environment variable HISTFILE. When a user logs off a system, this information is flushed to a file in the user's home directory called ~/.bash_history. The benefit of this is that it allows users to go back to commands they've used before in different sessions. Adversaries may delete their commands from these logs by manually clearing the history (history -c) or deleting the bash history file rm ~/.bash_history.

Adversaries may also leverage a Network Device CLI on network devices to clear command history data (clear logging and/or clear history).[1] On ESXi servers, command history may be manually removed from the `/var/log/shell.log` file.[2]

On Windows hosts, PowerShell has two different command history providers: the built-in history and the command history managed by the PSReadLine module. The built-in history only tracks the commands used in the current session. This command history is not available to other sessions and is deleted when the session ends.

The PSReadLine command history tracks the commands used in all PowerShell sessions and writes them to a file ($env:APPDATA\Microsoft\Windows\PowerShell\PSReadLine\ConsoleHost_history.txt by default). This history file is available to all sessions and contains all past history since the file is not deleted when the session ends.[3]

Adversaries may run the PowerShell command Clear-History to flush the entire command history from a current PowerShell session. This, however, will not delete/flush the ConsoleHost_history.txt file. Adversaries may also delete the ConsoleHost_history.txt file or edit its contents to hide PowerShell commands they have run.[4][5]

Adversaries may clear system logs to hide evidence of an intrusion. macOS and Linux both keep track of system or user-initiated actions via system logs. The majority of native system logging is stored under the `/var/log/` directory. Subfolders in this directory categorize logs by their related functions, such as:[1]

* `/var/log/messages:`: General and system-related messages * `/var/log/secure or /var/log/auth.log`: Authentication logs * `/var/log/utmp or /var/log/wtmp`: Login records * `/var/log/kern.log`: Kernel logs * `/var/log/cron.log`: Crond logs * `/var/log/maillog`: Mail server logs * `/var/log/httpd/`: Web server access and error logs

Adversaries may modify mail and mail application data to remove evidence of their activity. Email applications allow users and other programs to export and delete mailbox data via command line tools or use of APIs. Mail application data can be emails, email metadata, or logs generated by the application or operating system, such as export requests.

Adversaries may manipulate emails and mailbox data to remove logs, artifacts, and metadata, such as evidence of Phishing/Internal Spearphishing, Email Collection, Mail Protocols for command and control, or email-based exfiltration such as Exfiltration Over Alternative Protocol. For example, to remove evidence on Exchange servers adversaries have used the ExchangePowerShell PowerShell module, including Remove-MailboxExportRequest to remove evidence of mailbox exports.[1][2] On Linux and macOS, adversaries may also delete emails through a command line utility called mail or use AppleScript to interact with APIs on macOS.[3][4]

Adversaries may also remove emails and metadata/headers indicative of spam or suspicious activity (for example, through the use of organization-wide transport rules) to reduce the likelihood of malicious emails being detected by security products.[5]

Adversaries may clear or remove evidence of malicious network connections in order to clean up traces of their operations. Configuration settings as well as various artifacts that highlight connection history may be created on a system and/or in application logs from behaviors that require network connections, such as Remote Services or External Remote Services. Defenders may use these artifacts to monitor or otherwise analyze network connections created by adversaries.

Network connection history may be stored in various locations. For example, RDP connection history may be stored in Windows Registry values under [1]:

* HKEY_CURRENT_USER\Software\Microsoft\Terminal Server Client\Default * HKEY_CURRENT_USER\Software\Microsoft\Terminal Server Client\Servers

Windows may also store information about recent RDP connections in files such as C:\Users\\%username%\Documents\Default.rdp and `C:\Users\%username%\AppData\Local\Microsoft\Terminal Server Client\Cache\`.[2] Similarly, macOS and Linux hosts may store information highlighting connection history in system logs (such as those stored in `/Library/Logs` and/or `/var/log/`).[3][4][5]

Malicious network connections may also require changes to third-party applications or network configuration settings, such as Disable or Modify System Firewall or tampering to enable Proxy. Adversaries may delete or modify this data to conceal indicators and/or impede defensive analysis.

Adversaries may clear artifacts associated with previously established persistence on a host system to remove evidence of their activity. This may involve various actions, such as removing services, deleting executables, Modify Registry, Plist File Modification, or other methods of cleanup to prevent defenders from collecting evidence of their persistent presence.[1] Adversaries may also delete accounts previously created to maintain persistence (i.e. Create Account).[2]

In some instances, artifacts of persistence may also be removed once an adversary’s persistence is executed in order to prevent errors with the new instance of the malware.[3]

Adversaries may collect data stored in the clipboard from users copying information within or between applications.

For example, on Windows adversaries can access clipboard data by using clip.exe or Get-Clipboard.[1][2][3] Additionally, adversaries may monitor then replace users’ clipboard with their data (e.g., Transmitted Data Manipulation).[4]

macOS and Linux also have commands, such as pbpaste, to grab clipboard contents.[5]

Adversaries may obfuscate content during command execution to impede detection. Command-line obfuscation is a method of making strings and patterns within commands and scripts more difficult to signature and analyze. This type of obfuscation can be included within commands executed by delivered payloads (e.g., Phishing and Drive-by Compromise) or interactively via Command and Scripting Interpreter.[1][2]

For example, adversaries may abuse syntax that utilizes various symbols and escape characters (such as spacing, `^`, `+`. `$`, and `%`) to make commands difficult to analyze while maintaining the same intended functionality.[3] Many languages support built-in obfuscation in the form of base64 or URL encoding.[4] Adversaries may also manually implement command obfuscation via string splitting (`“Wor”+“d.Application”`), order and casing of characters (`rev <<<'dwssap/cte/ tac'`), globing (`mkdir -p '/tmp/:&$NiA'`), as well as various tricks involving passing strings through tokens/environment variables/input streams.[5][6]

Adversaries may also use tricks such as directory traversals to obfuscate references to the binary being invoked by a command (`C:\voi\pcw\..\..\Windows\tei\qs\k\..\..\..\system32\erool\..\wbem\wg\je\..\..\wmic.exe shadowcopy delete`).[7]

Tools such as Invoke-Obfuscation and Invoke-DOSfucation have also been used to obfuscate commands.[8][9]

Adversaries may abuse command and script interpreters to execute commands, scripts, or binaries. These interfaces and languages provide ways of interacting with computer systems and are a common feature across many different platforms. Most systems come with some built-in command-line interface and scripting capabilities, for example, macOS and Linux distributions include some flavor of Unix Shell while Windows installations include the Windows Command Shell and PowerShell.

There are also cross-platform interpreters such as Python, as well as those commonly associated with client applications such as JavaScript and Visual Basic.

Adversaries may abuse these technologies in various ways as a means of executing arbitrary commands. Commands and scripts can be embedded in Initial Access payloads delivered to victims as lure documents or as secondary payloads downloaded from an existing C2. Adversaries may also execute commands through interactive terminals/shells, as well as utilize various Remote Services in order to achieve remote Execution.[1][2][3]

Adversaries can perform command and control between compromised hosts on potentially disconnected networks using removable media to transfer commands from system to system.[1] Both systems would need to be compromised, with the likelihood that an Internet-connected system was compromised first and the second through lateral movement by Replication Through Removable Media. Commands and files would be relayed from the disconnected system to the Internet-connected system to which the adversary has direct access.

Adversaries may attempt to make payloads difficult to discover and analyze by delivering files to victims as uncompiled code. Text-based source code files may subvert analysis and scrutiny from protections targeting executables/binaries. These payloads will need to be compiled before execution; typically via native utilities such as ilasm.exe[1], csc.exe, or GCC/MinGW.[2]

Source code payloads may also be encrypted, encoded, and/or embedded within other files, such as those delivered as a Phishing. Payloads may also be delivered in formats unrecognizable and inherently benign to the native OS (ex: EXEs on macOS/Linux) before later being (re)compiled into a proper executable binary with a bundled compiler and execution framework.[3]

Adversaries may modify component firmware to persist on systems. Some adversaries may employ sophisticated means to compromise computer components and install malicious firmware that will execute adversary code outside of the operating system and main system firmware or BIOS. This technique may be similar to System Firmware but conducted upon other system components/devices that may not have the same capability or level of integrity checking.

Malicious component firmware could provide both a persistent level of access to systems despite potential typical failures to maintain access and hard disk re-images, as well as a way to evade host software-based defenses and integrity checks.

Adversaries may use compression to obfuscate their payloads or files. Compressed file formats such as ZIP, gzip, 7z, and RAR can compress and archive multiple files together to make it easier and faster to transfer files. In addition to compressing files, adversaries may also compress shellcode directly - for example, in order to store it in a Windows Registry key (i.e., Fileless Storage).[1]

In order to further evade detection, adversaries may combine multiple ZIP files into one archive. This process of concatenation creates an archive that appears to be a single archive but in fact contains the central directories of the embedded archives. Some ZIP readers, such as 7zip, may not be able to identify concatenated ZIP files and miss the presence of the malicious payload.[2]

File archives may be sent as one Spearphishing Attachment through email. Adversaries have sent malicious payloads as archived files to encourage the user to interact with and extract the malicious payload onto their system (i.e., Malicious File).[3] However, some file compression tools, such as 7zip, can be used to produce self-extracting archives. Adversaries may send self-extracting archives to hide the functionality of their payload and launch it without requiring multiple actions from the user.[4]

Compression may be used in combination with Encrypted/Encoded File where compressed files are encrypted and password-protected.

Adversaries may manipulate hardware components in products prior to receipt by a final consumer for the purpose of data or system compromise. By modifying hardware or firmware in the supply chain, adversaries can insert a backdoor into consumer networks that may be difficult to detect and give the adversary a high degree of control over the system. Hardware backdoors may be inserted into various devices, such as servers, workstations, network infrastructure, or peripherals.

Adversaries may modify host software binaries to establish persistent access to systems. Software binaries/executables provide a wide range of system commands or services, programs, and libraries. Common software binaries are SSH clients, FTP clients, email clients, web browsers, and many other user or server applications.

Adversaries may establish persistence though modifications to host software binaries. For example, an adversary may replace or otherwise infect a legitimate application binary (or support files) with a backdoor. Since these binaries may be routinely executed by applications or the user, the adversary can leverage this for persistent access to the host. An adversary may also modify a software binary such as an SSH client in order to persistently collect credentials during logins (i.e., Modify Authentication Process).[1]

An adversary may also modify an existing binary by patching in malicious functionality (e.g., IAT Hooking/Entry point patching)[2] prior to the binary’s legitimate execution. For example, an adversary may modify the entry point of a binary to point to malicious code patched in by the adversary before resuming normal execution flow.[3]

After modifying a binary, an adversary may attempt to impair defenses by preventing it from updating (e.g., via the `yum-versionlock` command or `versionlock.list` file in Linux systems that use the yum package manager).[1]

Adversaries may manipulate software dependencies and development tools prior to receipt by a final consumer for the purpose of data or system compromise. Applications often depend on external software to function properly. Popular open source projects that are used as dependencies in many applications, such as pip and NPM packages, may be targeted as a means to add malicious code to users of the dependency.[1][2][3] This may also include abandoned packages, which in some cases could be re-registered by threat actors after being removed by adversaries.[4] Adversaries may also employ "typosquatting" or name-confusion by choosing names similar to existing popular libraries or packages in order to deceive a user.[5][6][7]

Additionally, CI/CD pipeline components, such as GitHub Actions, may be targeted in order to gain access to the building, testing, and deployment cycles of an application.[8] By adding malicious code into a GitHub action, a threat actor may be able to collect runtime credentials (e.g., via Proc Filesystem) or insert further malicious components into the build pipelines for a second-order supply chain compromise.[9] As GitHub Actions are often dependent on other GitHub Actions, threat actors may be able to infect a large number of repositories via the compromise of a single Action.[10]

Targeting may be specific to a desired victim set or may be distributed to a broad set of consumers but only move on to additional tactics on specific victims.

Adversaries may manipulate application software prior to receipt by a final consumer for the purpose of data or system compromise. Supply chain compromise of software can take place in a number of ways, including manipulation of the application source code, manipulation of the update/distribution mechanism for that software, or replacing compiled releases with a modified version.

Targeting may be specific to a desired victim set or may be distributed to a broad set of consumers but only move on to additional tactics on specific victims.[1][2]

Adversaries may leverage the compute resources of co-opted systems to complete resource-intensive tasks, which may impact system and/or hosted service availability.

One common purpose for Compute Hijacking is to validate transactions of cryptocurrency networks and earn virtual currency. Adversaries may consume enough system resources to negatively impact and/or cause affected machines to become unresponsive.[1] Servers and cloud-based systems are common targets because of the high potential for available resources, but user endpoint systems may also be compromised and used for Compute Hijacking and cryptocurrency mining.[2] Containerized environments may also be targeted due to the ease of deployment via exposed APIs and the potential for scaling mining activities by deploying or compromising multiple containers within an environment or cluster.[3][4]

Additionally, some cryptocurrency mining malware identify then kill off processes for competing malware to ensure it’s not competing for resources.[5]

Adversaries may gain access and continuously communicate with victims by injecting malicious content into systems through online network traffic. Rather than luring victims to malicious payloads hosted on a compromised website (i.e., Drive-by Target followed by Drive-by Compromise), adversaries may initially access victims through compromised data-transfer channels where they can manipulate traffic and/or inject their own content. These compromised online network channels may also be used to deliver additional payloads (i.e., Ingress Tool Transfer) and other data to already compromised systems.[1]

Adversaries may inject content to victim systems in various ways, including:

* From the middle, where the adversary is in-between legitimate online client-server communications (**Note:** this is similar but distinct from Adversary-in-the-Middle, which describes AiTM activity solely within an enterprise environment) [2] * From the side, where malicious content is injected and races to the client as a fake response to requests of a legitimate online server [3]

Content injection is often the result of compromised upstream communication channels, for example at the level of an internet service provider (ISP) as is the case with "lawful interception."[3][1][4]

Adversaries may create an account to maintain access to victim systems.[1] With a sufficient level of access, creating such accounts may be used to establish secondary credentialed access that do not require persistent remote access tools to be deployed on the system.

Accounts may be created on the local system or within a domain or cloud tenant. In cloud environments, adversaries may create accounts that only have access to specific services, which can reduce the chance of detection.

Adversaries may create or modify system-level processes to repeatedly execute malicious payloads as part of persistence. When operating systems boot up, they can start processes that perform background system functions. On Windows and Linux, these system processes are referred to as services.[1] On macOS, launchd processes known as Launch Daemon and Launch Agent are run to finish system initialization and load user specific parameters.[2]

Adversaries may install new services, daemons, or agents that can be configured to execute at startup or a repeatable interval in order to establish persistence. Similarly, adversaries may modify existing services, daemons, or agents to achieve the same effect.

Services, daemons, or agents may be created with administrator privileges but executed under root/SYSTEM privileges. Adversaries may leverage this functionality to create or modify system processes in order to escalate privileges.[3]

Adversaries may hook into Windows application programming interface (API) functions and Linux system functions to collect user credentials. Malicious hooking mechanisms may capture API or function calls that include parameters that reveal user authentication credentials.[1] Unlike Keylogging, this technique focuses specifically on API functions that include parameters that reveal user credentials.

In Windows, hooking involves redirecting calls to these functions and can be implemented via:

* **Hooks procedures**, which intercept and execute designated code in response to events such as messages, keystrokes, and mouse inputs.[2][3] * **Import address table (IAT) hooking**, which use modifications to a process’s IAT, where pointers to imported API functions are stored.[3][4][5] * **Inline hooking**, which overwrites the first bytes in an API function to redirect code flow.[3][6][5]

In Linux and macOS, adversaries may hook into system functions via the `LD_PRELOAD` (Linux) or `DYLD_INSERT_LIBRARIES` (macOS) environment variables, which enables loading shared libraries into a program’s address space. For example, an adversary may capture credentials by hooking into the `libc read` function leveraged by SSH or SCP.[7]

Adversaries may use credentials obtained from breach dumps of unrelated accounts to gain access to target accounts through credential overlap. Occasionally, large numbers of username and password pairs are dumped online when a website or service is compromised and the user account credentials accessed. The information may be useful to an adversary attempting to compromise accounts by taking advantage of the tendency for users to use the same passwords across personal and business accounts.

Credential stuffing is a risky option because it could cause numerous authentication failures and account lockouts, depending on the organization's login failure policies.

Typically, management services over commonly used ports are used when stuffing credentials. Commonly targeted services include the following:

* SSH (22/TCP) * Telnet (23/TCP) * FTP (21/TCP) * NetBIOS / SMB / Samba (139/TCP & 445/TCP) * LDAP (389/TCP) * Kerberos (88/TCP) * RDP / Terminal Services (3389/TCP) * HTTP/HTTP Management Services (80/TCP & 443/TCP) * MSSQL (1433/TCP) * Oracle (1521/TCP) * MySQL (3306/TCP) * VNC (5900/TCP)

In addition to management services, adversaries may "target single sign-on (SSO) and cloud-based applications utilizing federated authentication protocols," as well as externally facing email applications, such as Office 365.[1]

Adversaries may search local file systems and remote file shares for files containing insecurely stored credentials. These can be files created by users to store their own credentials, shared credential stores for a group of individuals, configuration files containing passwords for a system or service, or source code/binary files containing embedded passwords.

It is possible to extract passwords from backups or saved virtual machines through OS Credential Dumping.[1] Passwords may also be obtained from Group Policy Preferences stored on the Windows Domain Controller.[2]

In cloud and/or containerized environments, authenticated user and service account credentials are often stored in local configuration and credential files.[3] They may also be found as parameters to deployment commands in container logs.[4] In some cases, these files can be copied and reused on another machine or the contents can be read and then used to authenticate without needing to copy any files.[5]

Adversaries may search for common password storage locations to obtain user credentials.[1] Passwords are stored in several places on a system, depending on the operating system or application holding the credentials. There are also specific applications and services that store passwords to make them easier for users to manage and maintain, such as password managers and cloud secrets vaults. Once credentials are obtained, they can be used to perform lateral movement and access restricted information.