Techniques

An adversary performs C2 communications using multiple layers of encryption, typically (but not exclusively) tunneling a custom encryption scheme within a protocol encryption scheme such as HTTPS or SMTPS.

Adversaries may constrain execution or actions based on the presence of a mutex associated with malware. A mutex is a locking mechanism used to synchronize access to a resource. Only one thread or process can acquire a mutex at a given time.[1]

While local mutexes only exist within a given process, allowing multiple threads to synchronize access to a resource, system mutexes can be used to synchronize the activities of multiple processes.[1] By creating a unique system mutex associated with a particular malware, adversaries can verify whether or not a system has already been compromised.[2]

In Linux environments, malware may instead attempt to acquire a lock on a mutex file. If the malware is able to acquire the lock, it continues to execute; if it fails, it exits to avoid creating a second instance of itself.[3][4]

Mutex names may be hard-coded or dynamically generated using a predictable algorithm.[5]

Adversaries may attempt to access or create a copy of the Active Directory domain database in order to steal credential information, as well as obtain other information about domain members such as devices, users, and access rights. By default, the NTDS file (NTDS.dit) is located in %SystemRoot%\NTDS\Ntds.dit of a domain controller.[1]

In addition to looking for NTDS files on active Domain Controllers, adversaries may search for backups that contain the same or similar information.[2]

The following tools and techniques can be used to enumerate the NTDS file and the contents of the entire Active Directory hashes.

* Volume Shadow Copy * secretsdump.py * Using the in-built Windows tool, ntdsutil.exe * Invoke-NinjaCopy

Adversaries may use NTFS file attributes to hide their malicious data in order to evade detection. Every New Technology File System (NTFS) formatted partition contains a Master File Table (MFT) that maintains a record for every file/directory on the partition. [1] Within MFT entries are file attributes, [2] such as Extended Attributes (EA) and Data [known as Alternate Data Streams (ADSs) when more than one Data attribute is present], that can be used to store arbitrary data (and even complete files). [1] [3] [4] [5]

Adversaries may store malicious data or binaries in file attribute metadata instead of directly in files. This may be done to evade some defenses, such as static indicator scanning tools and anti-virus. [6] [4]

Every New Technology File System (NTFS) formatted partition contains a Master File Table (MFT) that maintains a record for every file/directory on the partition. [1] Within MFT entries are file attributes, [2] such as Extended Attributes (EA) and Data [known as Alternate Data Streams (ADSs) when more than one Data attribute is present], that can be used to store arbitrary data (and even complete files). [1] [3] [4] [5]

Adversaries may store malicious data or binaries in file attribute metadata instead of directly in files. This may be done to evade some defenses, such as static indicator scanning tools and anti-virus. [6] [4]

By responding to LLMNR/NBT-NS/mDNS network traffic, adversaries may spoof an authoritative source for name resolution to force communication with an adversary controlled system.[1] This activity may be used to collect or relay authentication materials.

Link-Local Multicast Name Resolution (LLMNR) and NetBIOS Name Service (NBT-NS) are Microsoft Windows components that serve as alternate methods of host identification. LLMNR is based upon the Domain Name System (DNS) format and allows hosts on the same local link to perform name resolution for other hosts. NBT-NS identifies systems on a local network by their NetBIOS name.[2][3]

Multicast Domain Name System(mDNS) is a zero-configuration service used to resolve hostnames to IP addresses with “.local” as a top-level domain. MDNS is based upon Domain Name System (DNS) format and allows hosts on the same network segment to perform name resolution for other hosts, using multicast.[4]

Adversaries can spoof an authoritative source for name resolution on a victim network by responding to LLMNR (UDP 5355)/NBT-NS (UDP 137)/mDNS (UDP 5353) traffic as if they know the identity of the requested host, effectively poisoning the service so that the victims will communicate with the adversary controlled system. If the requested host belongs to a resource that requires identification/authentication, the username and NTLMv2 hash will then be sent to the adversary controlled system. The adversary can then collect the hash information sent over the wire through tools that monitor the ports for traffic or through Network Sniffing and crack the hashes offline through Brute Force to obtain the plaintext passwords.

In some cases where an adversary has access to a system that is in the authentication path between systems or when automated scans that use credentials attempt to authenticate to an adversary controlled system, the NTLMv1/v2 hashes can be intercepted and relayed to access and execute code against a target system. The relay step can happen in conjunction with poisoning but may also be independent of it.[5][6] Additionally, adversaries may encapsulate the NTLMv1/v2 hashes into various other protocols, such as LDAP, MSSQL and HTTP, to expand and use multiple services with the valid NTLM response.

Several tools may be used to poison name services within local networks such as NBNSpoof, Metasploit, and Responder.[7][8][9]

Adversaries may interact with the native OS application programming interface (API) to execute behaviors. Native APIs provide a controlled means of calling low-level OS services within the kernel, such as those involving hardware/devices, memory, and processes.[1][2] These native APIs are leveraged by the OS during system boot (when other system components are not yet initialized) as well as carrying out tasks and requests during routine operations.

Adversaries may abuse these OS API functions as a means of executing behaviors. Similar to Command and Scripting Interpreter, the native API and its hierarchy of interfaces provide mechanisms to interact with and utilize various components of a victimized system.

Native API functions (such as NtCreateProcess) may be directed invoked via system calls / syscalls, but these features are also often exposed to user-mode applications via interfaces and libraries.[3][4][5] For example, functions such as the Windows API CreateProcess() or GNU fork() will allow programs and scripts to start other processes.[6][7] This may allow API callers to execute a binary, run a CLI command, load modules, etc. as thousands of similar API functions exist for various system operations.[8][9][10]

Higher level software frameworks, such as Microsoft .NET and macOS Cocoa, are also available to interact with native APIs. These frameworks typically provide language wrappers/abstractions to API functionalities and are designed for ease-of-use/portability of code.[11][12][13][14]

Adversaries may use assembly to directly or in-directly invoke syscalls in an attempt to subvert defensive sensors and detection signatures such as user mode API-hooks.[15] Adversaries may also attempt to tamper with sensors and defensive tools associated with API monitoring, such as unhooking monitored functions via Disable or Modify Tools.

Adversaries may use Android’s Native Development Kit (NDK) to write native functions that can achieve execution of binaries or functions. Like system calls on a traditional desktop operating system, native code achieves execution on a lower level than normal Android SDK calls.

The NDK allows developers to write native code in C or C++ that is compiled directly to machine code, avoiding all intermediate languages and steps in compilation that higher level languages, like Java, typically have. The Java Native Interface (JNI) is the component that allows Java functions in the Android app to call functions in a native library.[1]

Adversaries may also choose to use native functions to execute malicious code since native actions are typically much more difficult to analyze than standard, non-native behaviors.[2]

Adversaries may directly interact with the native OS application programming interface (API) to access system functions. Native APIs provide a controlled means of calling low-level OS services within the kernel, such as those involving hardware/devices, memory, and processes. [1] These native APIs are leveraged by the OS during system boot (when other system components are not yet initialized) as well as carrying out tasks and requests during routine operations.

Functionality provided by native APIs are often also exposed to user-mode applications via interfaces and libraries. For example, functions such as memcpy and direct operations on memory registers can be used to modify user and system memory space.

Netsh.exe (also referred to as Netshell) is a command-line scripting utility used to interact with the network configuration of a system. It contains functionality to add helper DLLs for extending functionality of the utility. [1] The paths to registered netsh.exe helper DLLs are entered into the Windows Registry at HKLM\SOFTWARE\Microsoft\Netsh.

Adversaries can use netsh.exe with helper DLLs to proxy execution of arbitrary code in a persistent manner when netsh.exe is executed automatically with another Persistence technique or if other persistent software is present on the system that executes netsh.exe as part of its normal functionality. Examples include some VPN software that invoke netsh.exe. [2]

Proof of concept code exists to load Cobalt Strike's payload using netsh.exe helper DLLs. [3]

Adversaries may establish persistence by executing malicious content triggered by Netsh Helper DLLs. Netsh.exe (also referred to as Netshell) is a command-line scripting utility used to interact with the network configuration of a system. It contains functionality to add helper DLLs for extending functionality of the utility.[1] The paths to registered netsh.exe helper DLLs are entered into the Windows Registry at HKLM\SOFTWARE\Microsoft\Netsh.

Adversaries can use netsh.exe helper DLLs to trigger execution of arbitrary code in a persistent manner. This execution would take place anytime netsh.exe is executed, which could happen automatically, with another persistence technique, or if other software (ex: VPN) is present on the system that executes netsh.exe as part of its normal functionality.[2][3]

Adversaries may bridge network boundaries by modifying a network device’s Network Address Translation (NAT) configuration. Malicious modifications to NAT may enable an adversary to bypass restrictions on traffic routing that otherwise separate trusted and untrusted networks.

Network devices such as routers and firewalls that connect multiple networks together may implement NAT during the process of passing packets between networks. When performing NAT, the network device will rewrite the source and/or destination addresses of the IP address header. Some network designs require NAT for the packets to cross the border device. A typical example of this is environments where internal networks make use of non-Internet routable addresses.[1]

When an adversary gains control of a network boundary device, they may modify NAT configurations to send traffic between two separated networks, or to obscure their activities. In network designs that require NAT to function, such modifications enable the adversary to overcome inherent routing limitations that would normally prevent them from accessing protected systems behind the border device. In network designs that do not require NAT, adversaries may use address translation to further obscure their activities, as changing the addresses of packets that traverse a network boundary device can make monitoring data transmissions more challenging for defenders.

Adversaries may use Patch System Image to change the operating system of a network device, implementing their own custom NAT mechanisms to further obscure their activities.

Adversaries may bridge network boundaries by compromising perimeter network devices or internal devices responsible for network segmentation. Breaching these devices may enable an adversary to bypass restrictions on traffic routing that otherwise separate trusted and untrusted networks.

Devices such as routers and firewalls can be used to create boundaries between trusted and untrusted networks. They achieve this by restricting traffic types to enforce organizational policy in an attempt to reduce the risk inherent in such connections. Restriction of traffic can be achieved by prohibiting IP addresses, layer 4 protocol ports, or through deep packet inspection to identify applications. To participate with the rest of the network, these devices can be directly addressable or transparent, but their mode of operation has no bearing on how the adversary can bypass them when compromised.

When an adversary takes control of such a boundary device, they can bypass its policy enforcement to pass normally prohibited traffic across the trust boundary between the two separated networks without hinderance. By achieving sufficient rights on the device, an adversary can reconfigure the device to allow the traffic they want, allowing them to then further achieve goals such as command and control via Multi-hop Proxy or exfiltration of data via Traffic Duplication. Adversaries may also target internal devices responsible for network segmentation and abuse these in conjunction with Internal Proxy to achieve the same goals.[1] In the cases where a border device separates two separate organizations, the adversary can also facilitate lateral movement into new victim environments.

Adversaries may perform network connection enumeration to discover information about device communication patterns. If an adversary can inspect the state of a network connection with tools, such as Netstat[1], in conjunction with System Firmware, then they can determine the role of certain devices on the network [2]. The adversary can also use Network Sniffing to watch network traffic for details about the source, destination, protocol, and content.

Adversaries may perform Network Denial of Service (DoS) attacks to degrade or block the availability of targeted resources to users. Network DoS can be performed by exhausting the network bandwidth services rely on. Example resources include specific websites, email services, DNS, and web-based applications. Adversaries have been observed conducting network DoS attacks for political purposes[1] and to support other malicious activities, including distraction[2], hacktivism, and extortion.[3]

A Network DoS will occur when the bandwidth capacity of the network connection to a system is exhausted due to the volume of malicious traffic directed at the resource or the network connections and network devices the resource relies on. For example, an adversary may send 10Gbps of traffic to a server that is hosted by a network with a 1Gbps connection to the internet. This traffic can be generated by a single system or multiple systems spread across the internet, which is commonly referred to as a distributed DoS (DDoS).

To perform Network DoS attacks several aspects apply to multiple methods, including IP address spoofing, and botnets.

Adversaries may use the original IP address of an attacking system, or spoof the source IP address to make the attack traffic more difficult to trace back to the attacking system or to enable reflection. This can increase the difficulty defenders have in defending against the attack by reducing or eliminating the effectiveness of filtering by the source address on network defense devices.

For DoS attacks targeting the hosting system directly, see Endpoint Denial of Service.

Adversaries may perform Network Denial of Service (DoS) attacks to degrade or block the availability of targeted resources to users. Network DoS can be performed by exhausting the network bandwidth that services rely on, or by jamming the signal going to or coming from devices.

A Network DoS will occur when an adversary is able to jam radio signals (e.g. Wi-Fi, cellular, GPS) around a device to prevent it from communicating. For example, to jam cellular signal, an adversary may use a handheld signal jammer, which jam devices within the jammer’s operational range.[1]

Usage of cellular jamming has been documented in several arrests reported in the news.[2][3][4][5]

Adversaries may use Patch System Image to hard code a password in the operating system, thus bypassing of native authentication mechanisms for local accounts on network devices.

Modify System Image may include implanted code to the operating system for network devices to provide access for adversaries using a specific password. The modification includes a specific password which is implanted in the operating system image via the patch. Upon authentication attempts, the inserted code will first check to see if the user input is the password. If so, access is granted. Otherwise, the implanted code will pass the credentials on for verification of potentially valid credentials.[1]

Adversaries may abuse scripting or built-in command line interpreters (CLI) on network devices to execute malicious command and payloads. The CLI is the primary means through which users and administrators interact with the device in order to view system information, modify device operations, or perform diagnostic and administrative functions. CLIs typically contain various permission levels required for different commands.

Scripting interpreters automate tasks and extend functionality beyond the command set included in the network OS. The CLI and scripting interpreter are accessible through a direct console connection, or through remote means, such as telnet or SSH.

Adversaries can use the network CLI to change how network devices behave and operate. The CLI may be used to manipulate traffic flows to intercept or manipulate data, modify startup configuration parameters to load malicious system software, or to disable security features or logging to avoid detection.[1]

Adversaries may access network configuration files to collect sensitive data about the device and the network. The network configuration is a file containing parameters that determine the operation of the device. The device typically stores an in-memory copy of the configuration while operating, and a separate configuration on non-volatile storage to load after device reset. Adversaries can inspect the configuration files to reveal information about the target network and its layout, the network device and its software, or identifying legitimate accounts and credentials for later use.

Adversaries can use common management tools and protocols, such as Simple Network Management Protocol (SNMP) and Smart Install (SMI), to access network configuration files.[1][2] These tools may be used to query specific data from a configuration repository or configure the device to export the configuration for later analysis.

Adversaries may disable network device-based firewall mechanisms entirely or add, delete, or modify particular rules in order to bypass controls limiting network usage.

Adversaries may obtain access to devices such as routers, switches, or other perimeter/network devices and change access control lists (ACLs), security zones, or policy rules to permit otherwise blocked traffic. For example, adversaries may add new network firewall rules to allow access to all internal network subnets without restrictions. Allowing access to internal network subsets may enable unrestricted inbound/outbound connectivity or open paths for command and control and lateral movement.

Adversaries may obtain access to network device management interfaces via Valid Accounts or by exploiting vulnerabilities. In some cases, threat actors may target firewalls and other network infrastructure that are exposed to the internet by leveraging weaknesses in public-facing applications (Exploit Public-Facing Application).[1]

Adversaries may also modify host networking configurations that indirectly manipulate system firewalls, such as adjusting interface bandwidth or network connection request thresholds.

Adversaries may compromise third-party network devices that can be used during targeting. Network devices, such as small office/home office (SOHO) routers, may be compromised where the adversary's ultimate goal is not Initial Access to that environment, but rather to leverage these devices to support additional targeting.

Once an adversary has control, compromised network devices can be used to launch additional operations, such as hosting payloads for Phishing campaigns (i.e., Link Target) or enabling the required access to execute Content Injection operations. Adversaries may also be able to harvest reusable credentials (i.e., Valid Accounts) from compromised network devices.

Adversaries often target Internet-facing edge devices and related network appliances that specifically do not support robust host-based defenses.[1][2]

Compromised network devices may be used to support subsequent Command and Control activity, such as Hide Infrastructure through an established Proxy and/or Botnet network.[3]

Adversaries may use device sensors to collect information about nearby networks, such as Wi-Fi and Bluetooth.

Adversaries may use network logon scripts automatically executed at logon initialization to establish persistence. Network logon scripts can be assigned using Active Directory or Group Policy Objects.[1] These logon scripts run with the privileges of the user they are assigned to. Depending on the systems within the network, initializing one of these scripts could apply to more than one or potentially all systems. Adversaries may use these scripts to maintain persistence on a network. Depending on the access configuration of the logon scripts, either local credentials or an administrator account may be necessary.

Adversaries may register malicious network provider dynamic link libraries (DLLs) to capture cleartext user credentials during the authentication process. Network provider DLLs allow Windows to interface with specific network protocols and can also support add-on credential management functions.[1] During the logon process, Winlogon (the interactive logon module) sends credentials to the local `mpnotify.exe` process via RPC. The `mpnotify.exe` process then shares the credentials in cleartext with registered credential managers when notifying that a logon event is happening.[2][3][4]

Adversaries can configure a malicious network provider DLL to receive credentials from `mpnotify.exe`.[5] Once installed as a credential manager (via the Registry), a malicious DLL can receive and save credentials each time a user logs onto a Windows workstation or domain via the `NPLogonNotify()` function.[4]

Adversaries may target planting malicious network provider DLLs on systems known to have increased logon activity and/or administrator logon activity, such as servers and domain controllers.[2]

Adversaries may gather information about the victim's network security appliances that can be used during targeting. Information about network security appliances may include a variety of details, such as the existence and specifics of deployed firewalls, content filters, and proxies/bastion hosts. Adversaries may also target information about victim network-based intrusion detection systems (NIDS) or other appliances related to defensive cybersecurity operations.

Adversaries may gather this information in various ways, such as direct collection actions via Active Scanning or Phishing for Information.[1] Information about network security appliances may also be exposed to adversaries via online or other accessible data sets (ex: Search Victim-Owned Websites). Gathering this information may reveal opportunities for other forms of reconnaissance (ex: Search Open Technical Databases or Search Open Websites/Domains), establishing operational resources (ex: Develop Capabilities or Obtain Capabilities), and/or initial access (ex: External Remote Services).