Techniques

Adversaries may take advantage of trusted developer utilities to proxy execution of malicious payloads. There are many utilities used for software development related tasks that can be used to execute code in various forms to assist in development, debugging, and reverse engineering.[1][2][3][4] These utilities may often be signed with legitimate certificates that allow them to execute on a system and proxy execution of malicious code through a trusted process that effectively bypasses application control solutions.

Smart App Control is a feature of Windows that blocks applications it considers potentially malicious from running by verifying unsigned applications against a known safe list from a Microsoft cloud service before executing them.[5] However, adversaries may leverage "reputation hijacking" to abuse an operating system’s trust of safe, signed applications that support the execution of arbitrary code. By leveraging Trusted Developer Utilities Proxy Execution to run their malicious code, adversaries may bypass Smart App Control protections.[6]

Adversaries may breach or otherwise leverage organizations who have access to intended victims. Access through trusted third party relationship abuses an existing connection that may not be protected or receives less scrutiny than standard mechanisms of gaining access to a network.

Organizations often grant elevated access to second or third-party external providers in order to allow them to manage internal systems as well as cloud-based environments. Some examples of these relationships include IT services contractors, managed security providers, infrastructure contractors (e.g. HVAC, elevators, physical security). The third-party provider's access may be intended to be limited to the infrastructure being maintained, but may exist on the same network as the rest of the enterprise. As such, Valid Accounts used by the other party for access to internal network systems may be compromised and used.[1]

In Office 365 environments, organizations may grant Microsoft partners or resellers delegated administrator permissions. By compromising a partner or reseller account, an adversary may be able to leverage existing delegated administrator relationships or send new delegated administrator offers to clients in order to gain administrative control over the victim tenant.[2]

Adversaries may register Uniform Resource Identifiers (URIs) to intercept sensitive data.

Applications regularly register URIs with the operating system to act as a response handler for various actions, such as logging into an app using an external account via single sign-on. This allows redirections to that specific URI to be intercepted by the application. If an adversary were to register for a URI that was already in use by a genuine application, the adversary may be able to intercept data intended for the genuine application or perform a phishing attack against the genuine application. Intercepted data may include OAuth authorization codes or tokens that could be used by the adversary to gain access to protected resources.[1][2]

Adversaries may maintain persistence through executing malicious content triggered using udev rules. Udev is the Linux kernel device manager that dynamically manages device nodes, handles access to pseudo-device files in the `/dev` directory, and responds to hardware events, such as when external devices like hard drives or keyboards are plugged in or removed. Udev uses rule files with `match keys` to specify the conditions a hardware event must meet and `action keys` to define the actions that should follow. Root permissions are required to create, modify, or delete rule files located in `/etc/udev/rules.d/`, `/run/udev/rules.d/`, `/usr/lib/udev/rules.d/`, `/usr/local/lib/udev/rules.d/`, and `/lib/udev/rules.d/`. Rule priority is determined by both directory and by the digit prefix in the rule filename.[1][2]

Adversaries may abuse the udev subsystem by adding or modifying rules in udev rule files to execute malicious content. For example, an adversary may configure a rule to execute their binary each time the pseudo-device file, such as `/dev/random`, is accessed by an application. Although udev is limited to running short tasks and is restricted by systemd-udevd's sandbox (blocking network and filesystem access), attackers may use scripting commands under the action key `RUN+=` to detach and run the malicious content’s process in the background to bypass these controls.[3]

Adversaries may send unauthorized messages to ICS systems and devices to evade defenses or manipulate processes. Unauthorized messages can be categorized as either reporting messages that contain telemetry data about the current state of systems, devices, and processes or as command messages which instruct systems and devices on how to operate. By injecting unauthorized messages, adversaries can make it appear as if everything is working correctly when it isn’t, trigger alarms to misdirect personnel or impact processes, and manipulate controls to disrupt processes.[1]

Adversaries may send unauthorized messages in an ICS environment using software found within the environment (living-off-the-land, vendor-specific interfaces, etc.), custom tooling leveraging OT protocols and libraries, or by positioning themselves between systems and devices and injecting messages into the communications such as the case with an Adversary-in-the-Middle attack.

Adversaries may include functionality in malware that uninstalls the malicious application from the device. This can be achieved by: * Abusing device owner permissions to perform silent uninstallation using device owner API calls. * Abusing root permissions to delete files from the filesystem. * Abusing the accessibility service. This requires sending an intent to the system to request uninstallation, and then abusing the accessibility service to click the proper places on the screen to confirm uninstallation.

Adversaries may abuse Unix shell commands and scripts for execution. Unix shells are the primary command prompt on Linux, macOS, and ESXi systems, though many variations of the Unix shell exist (e.g. sh, ash, bash, zsh, etc.) depending on the specific OS or distribution.[1][2] Unix shells can control every aspect of a system, with certain commands requiring elevated privileges.

Unix shells also support scripts that enable sequential execution of commands as well as other typical programming operations such as conditionals and loops. Common uses of shell scripts include long or repetitive tasks, or the need to run the same set of commands on multiple systems.

Adversaries may abuse Unix shells to execute various commands or payloads. Interactive shells may be accessed through command and control channels or during lateral movement such as with SSH. Adversaries may also leverage shell scripts to deliver and execute multiple commands on victims or as part of payloads used for persistence.

Some systems, such as embedded devices, lightweight Linux distributions, and ESXi servers, may leverage stripped-down Unix shells via Busybox, a small executable that contains a variety of tools, including a simple shell.

Adversaries may abuse Unix shell commands and scripts for execution. Unix shells are the underlying command prompts on Android and iOS devices. Unix shells can control every aspect of a system, with certain commands requiring elevated privileges that are only accessible if the device has been rooted or jailbroken.

Unix shells also support scripts that enable sequential execution of commands as well as other typical programming operations such as conditionals and loops. Common uses of shell scripts include long or repetitive tasks, or the need to run the same set of commands on multiple systems.

Adversaries may abuse Unix shells to execute various commands or payloads. Interactive shells may be accessed through command and control channels or during lateral movement such as with SSH. Adversaries may also leverage shell scripts to deliver and execute multiple commands on victims or as part of payloads used for persistence.

If the device has been rooted or jailbroken, adversaries may locate and invoke a superuser binary to elevate their privileges and interact with the system as the root user. This dangerous level of permissions allows the adversary to run special commands and modify protected system files.

Adversaries may establish persistence through executing malicious commands triggered by a user’s shell. User Unix Shells execute several configuration scripts at different points throughout the session based on events. For example, when a user opens a command-line interface or remotely logs in (such as via SSH) a login shell is initiated. The login shell executes scripts from the system (/etc) and the user’s home directory (~/) to configure the environment. All login shells on a system use /etc/profile when initiated. These configuration scripts run at the permission level of their directory and are often used to set environment variables, create aliases, and customize the user’s environment. When the shell exits or terminates, additional shell scripts are executed to ensure the shell exits appropriately.

Adversaries may attempt to establish persistence by inserting commands into scripts automatically executed by shells. Using bash as an example, the default shell for most GNU/Linux systems, adversaries may add commands that launch malicious binaries into the /etc/profile and /etc/profile.d files.[1][2] These files typically require root permissions to modify and are executed each time any shell on a system launches. For user level permissions, adversaries can insert malicious commands into ~/.bash_profile, ~/.bash_login, or ~/.profile which are sourced when a user opens a command-line interface or connects remotely.[3][4] Since the system only executes the first existing file in the listed order, adversaries have used ~/.bash_profile to ensure execution. Adversaries have also leveraged the ~/.bashrc file which is additionally executed if the connection is established remotely or an additional interactive shell is opened, such as a new tab in the command-line interface.[5][3][6][7] Some malware targets the termination of a program to trigger execution, adversaries can use the ~/.bash_logout file to execute malicious commands at the end of a session.

For macOS, the functionality of this technique is similar but may leverage zsh, the default shell for macOS 10.15+. When the Terminal.app is opened, the application launches a zsh login shell and a zsh interactive shell. The login shell configures the system environment using /etc/profile, /etc/zshenv, /etc/zprofile, and /etc/zlogin.[8][9][10][11] The login shell then configures the user environment with ~/.zprofile and ~/.zlogin. The interactive shell uses the ~/.zshrc to configure the user environment. Upon exiting, /etc/zlogout and ~/.zlogout are executed. For legacy programs, macOS executes /etc/bashrc on startup.

Adversaries may search compromised systems to find and obtain insecurely stored credentials. These credentials can be stored and/or misplaced in many locations on a system, including plaintext files (e.g. Shell History), operating system or application-specific repositories (e.g. Credentials in Registry), or other specialized files/artifacts (e.g. Private Keys).[1]

Adversaries may create cloud instances in unused geographic service regions in order to evade detection. Access is usually obtained through compromising accounts used to manage cloud infrastructure.

Cloud service providers often provide infrastructure throughout the world in order to improve performance, provide redundancy, and allow customers to meet compliance requirements. Oftentimes, a customer will only use a subset of the available regions and may not actively monitor other regions. If an adversary creates resources in an unused region, they may be able to operate undetected.

A variation on this behavior takes advantage of differences in functionality across cloud regions. An adversary could utilize regions which do not support advanced detection services in order to avoid detection of their activity.

An example of adversary use of unused AWS regions is to mine cryptocurrency through Resource Hijacking, which can cost organizations substantial amounts of money over time depending on the processing power used.[1]

Adversaries may upload malware to third-party or adversary controlled infrastructure to make it accessible during targeting. Malicious software can include payloads, droppers, post-compromise tools, backdoors, and a variety of other malicious content. Adversaries may upload malware to support their operations, such as making a payload available to a victim network to enable Ingress Tool Transfer by placing it on an Internet accessible web server.

Malware may be placed on infrastructure that was previously purchased/rented by the adversary (Acquire Infrastructure) or was otherwise compromised by them (Compromise Infrastructure). Malware can also be staged on web services, such as GitHub or Pastebin; hosted on the InterPlanetary File System (IPFS), where decentralized content storage makes the removal of malicious files difficult; or saved on the blockchain as smart contracts, which are resilient against takedowns that would affect traditional infrastructure.[1][2][3][4]

Adversaries may upload backdoored files, such as software packages, application binaries, virtual machine images, or container images, to third-party software stores, package libraries, extension marketplaces, or repositories (ex: GitHub, CNET, AWS Community AMIs, Docker Hub, PyPi, NPM).[5] By chance encounter, victims may directly download/install these backdoored files via User Execution. Masquerading, including typosquatting legitimate software, may increase the chance of users mistakenly executing these files.

Adversaries may upload tools to third-party or adversary controlled infrastructure to make it accessible during targeting. Tools can be open or closed source, free or commercial. Tools can be used for malicious purposes by an adversary, but (unlike malware) were not intended to be used for those purposes (ex: PsExec). Adversaries may upload tools to support their operations, such as making a tool available to a victim network to enable Ingress Tool Transfer by placing it on an Internet accessible web server.

Tools may be placed on infrastructure that was previously purchased/rented by the adversary (Acquire Infrastructure) or was otherwise compromised by them (Compromise Infrastructure).[1] Tools can also be staged on web services, such as an adversary controlled GitHub repo, or on Platform-as-a-Service offerings that enable users to easily provision applications.[2][3][4]

Adversaries can avoid the need to upload a tool by having compromised victim machines download the tool directly from a third-party hosting location (ex: a non-adversary controlled GitHub repo), including the original hosting site of the tool.

Adversaries may use alternate authentication material, such as password hashes, Kerberos tickets, and application access tokens, in order to move laterally within an environment and bypass normal system access controls.

Authentication processes generally require a valid identity (e.g., username) along with one or more authentication factors (e.g., password, pin, physical smart card, token generator, etc.). Alternate authentication material is legitimately generated by systems after a user or application successfully authenticates by providing a valid identity and the required authentication factor(s). Alternate authentication material may also be generated during the identity creation process.[1][2]

Caching alternate authentication material allows the system to verify an identity has successfully authenticated without asking the user to reenter authentication factor(s). Because the alternate authentication must be maintained by the system—either in memory or on disk—it may be at risk of being stolen through Credential Access techniques. By stealing alternate authentication material, adversaries are able to bypass system access controls and authenticate to systems without knowing the plaintext password or any additional authentication factors.

Adversaries may employ various user activity checks to detect and avoid virtualization and analysis environments. This may include changing behaviors based on the results of checks for the presence of artifacts indicative of a virtual machine environment (VME) or sandbox. If the adversary detects a VME, they may alter their malware to disengage from the victim or conceal the core functions of the implant. They may also search for VME artifacts before dropping secondary or additional payloads. Adversaries may use the information learned from Virtualization/Sandbox Evasion during automated discovery to shape follow-on behaviors.[1]

Adversaries may search for user activity on the host based on variables such as the speed/frequency of mouse movements and clicks [2] , browser history, cache, bookmarks, or number of files in common directories such as home or the desktop. Other methods may rely on specific user interaction with the system before the malicious code is activated, such as waiting for a document to close before activating a macro [3] or waiting for a user to double click on an embedded image to activate.[4]

Adversaries may attempt to avoid detection by hiding malicious behavior from the user. By doing this, an adversary’s modifications would most likely remain installed on the device for longer, allowing the adversary to continue to operate on that device.

While there are many ways this can be accomplished, one method is by using the device’s sensors. By utilizing the various motion sensors on a device, such as accelerometer or gyroscope, an application could detect that the device is being interacted with. That way, the application could continue to run while the device is not in use but cease operating while the user is using the device, hiding anything that would indicate malicious activity was ongoing. Accessing the sensors in this way does not require any permissions from the user, so it would be completely transparent.

An adversary may rely upon specific actions by a user in order to gain execution. Users may be subjected to social engineering to get them to execute malicious code by, for example, opening a malicious document file or link. These user actions will typically be observed as follow-on behavior from forms of Phishing.

While User Execution frequently occurs shortly after Initial Access it may occur at other phases of an intrusion, such as when an adversary places a file in a shared directory or on a user's desktop hoping that a user will click on it. This activity may also be seen shortly after Internal Spearphishing.

Adversaries may also deceive users into performing actions such as:

* Enabling Remote Access Tools, allowing direct control of the system to the adversary * Running malicious JavaScript in their browser, allowing adversaries to Steal Web Session Cookies[1][2] * Downloading and executing malware for User Execution * Coerceing users to copy, paste, and execute malicious code manually[3][4]

For example, tech support scams can be facilitated through Phishing, vishing, or various forms of user interaction. Adversaries can use a combination of these methods, such as spoofing and promoting toll-free numbers or call centers that are used to direct victims to malicious websites, to deliver and execute payloads containing malware or Remote Access Tools.[5]

Adversaries may rely on a targeted organizations user interaction for the execution of malicious code. User interaction may consist of installing applications, opening email attachments, or granting higher permissions to documents.

Adversaries may embed malicious code or visual basic code into files such as Microsoft Word and Excel documents or software installers. [1] Execution of this code requires that the user enable scripting or write access within the document. Embedded code may not always be noticeable to the user especially in cases of trojanized software. [2]

A Chinese spearphishing campaign running from December 9, 2011 through February 29, 2012 delivered malware through spearphishing attachments which required user action to achieve execution. [3]

Adversaries may hide malicious Visual Basic for Applications (VBA) payloads embedded within MS Office documents by replacing the VBA source code with benign data.[1]

MS Office documents with embedded VBA content store source code inside of module streams. Each module stream has a PerformanceCache that stores a separate compiled version of the VBA source code known as p-code. The p-code is executed when the MS Office version specified in the _VBA_PROJECT stream (which contains the version-dependent description of the VBA project) matches the version of the host MS Office application.[2][3]

An adversary may hide malicious VBA code by overwriting the VBA source code location with zero’s, benign code, or random bytes while leaving the previously compiled malicious p-code. Tools that scan for malicious VBA source code may be bypassed as the unwanted code is hidden in the compiled p-code. If the VBA source code is removed, some tools might even think that there are no macros present. If there is a version match between the _VBA_PROJECT stream and host MS Office application, the p-code will be executed, otherwise the benign VBA source code will be decompressed and recompiled to p-code, thus removing malicious p-code and potentially bypassing dynamic analysis.[4][1][5]

Adversaries may inject malicious code into processes via VDSO hijacking in order to evade process-based defenses as well as possibly elevate privileges. Virtual dynamic shared object (vdso) hijacking is a method of executing arbitrary code in the address space of a separate live process.

VDSO hijacking involves redirecting calls to dynamically linked shared libraries. Memory protections may prevent writing executable code to a process via Ptrace System Calls. However, an adversary may hijack the syscall interface code stubs mapped into a process from the vdso shared object to execute syscalls to open and map a malicious shared object. This code can then be invoked by redirecting the execution flow of the process via patched memory address references stored in a process' global offset table (which store absolute addresses of mapped library functions).[1][2][3][4]

Running code in the context of another process may allow access to the process's memory, system/network resources, and possibly elevated privileges. Execution via VDSO hijacking may also evade detection from security products since the execution is masked under a legitimate process.

Adversaries may use Valid Accounts to remotely control machines using Virtual Network Computing (VNC). VNC is a platform-independent desktop sharing system that uses the RFB (“remote framebuffer”) protocol to enable users to remotely control another computer’s display by relaying the screen, mouse, and keyboard inputs over the network.[1]

VNC differs from Remote Desktop Protocol as VNC is screen-sharing software rather than resource-sharing software. By default, VNC uses the system's authentication, but it can be configured to use credentials specific to VNC.[2][3]

Adversaries may abuse VNC to perform malicious actions as the logged-on user such as opening documents, downloading files, and running arbitrary commands. An adversary could use VNC to remotely control and monitor a system to collect data and information to pivot to other systems within the network. Specific VNC libraries/implementations have also been susceptible to brute force attacks and memory usage exploitation.[4][5][6][7][8][9]

Adversaries may obtain and abuse credentials of existing accounts as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion. Compromised credentials may be used to bypass access controls placed on various resources on systems within the network and may even be used for persistent access to remote systems and externally available services, such as VPNs, Outlook Web Access, network devices, and remote desktop.[1] Compromised credentials may also grant an adversary increased privilege to specific systems or access to restricted areas of the network. Adversaries may choose not to use malware or tools in conjunction with the legitimate access those credentials provide to make it harder to detect their presence.

In some cases, adversaries may abuse inactive accounts: for example, those belonging to individuals who are no longer part of an organization. Using these accounts may allow the adversary to evade detection, as the original account user will not be present to identify any anomalous activity taking place on their account.[2]

The overlap of permissions for local, domain, and cloud accounts across a network of systems is of concern because the adversary may be able to pivot across accounts and systems to reach a high level of access (i.e., domain or enterprise administrator) to bypass access controls set within the enterprise.[3]

Adversaries may steal the credentials of a specific user or service account using credential access techniques. In some cases, default credentials for control system devices may be publicly available. Compromised credentials may be used to bypass access controls placed on various resources on hosts and within the network, and may even be used for persistent access to remote systems. Compromised and default credentials may also grant an adversary increased privilege to specific systems and devices or access to restricted areas of the network. Adversaries may choose not to use malware or tools, in conjunction with the legitimate access those credentials provide, to make it harder to detect their presence or to control devices and send legitimate commands in an unintended way.

Adversaries may also create accounts, sometimes using predefined account names and passwords, to provide a means of backup access for persistence. [1]

The overlap of credentials and permissions across a network of systems is of concern because the adversary may be able to pivot across accounts and systems to reach a high level of access (i.e., domain or enterprise administrator) and possibly between the enterprise and operational technology environments. Adversaries may be able to leverage valid credentials from one system to gain access to another system.

Adversaries may abuse verclsid.exe to proxy execution of malicious code. Verclsid.exe is known as the Extension CLSID Verification Host and is responsible for verifying each shell extension before they are used by Windows Explorer or the Windows Shell.[1]

Adversaries may abuse verclsid.exe to execute malicious payloads. This may be achieved by running verclsid.exe /S /C {CLSID}, where the file is referenced by a Class ID (CLSID), a unique identification number used to identify COM objects. COM payloads executed by verclsid.exe may be able to perform various malicious actions, such as loading and executing COM scriptlets (SCT) from remote servers (similar to Regsvr32). Since the binary may be signed and/or native on Windows systems, proxying execution via verclsid.exe may bypass application control solutions that do not account for its potential abuse.[2][3][4][5]

An adversary can leverage a computer's peripheral devices (e.g., integrated cameras or webcams) or applications (e.g., video call services) to capture video recordings for the purpose of gathering information. Images may also be captured from devices or applications, potentially in specified intervals, in lieu of video files.

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 video or images. Video or image files may be written to disk and exfiltrated later. This technique differs from Screen Capture due to use of specific devices or applications for video recording rather than capturing the victim's screen.

In macOS, there are a few different malware samples that record the user's webcam such as FruitFly and Proton. [1]