Presented by: Ashwin (Microsoft Azure MVP)
ABK is a downloader that has been used by BRONZE BUTLER since at least 2019.
Source:
MITRE ATT&CK® Matrix for Enterprise
Now, let's see the details around the series of events associated with this software in chronological order, and how we can work to mitigate or detect these threats.
ABK has the ability to use cmd to run a Portable Executable (PE) on the compromised host.
Adversaries may abuse the Windows command shell for execution. The Windows command shell (cmd) is the primary command prompt on Windows systems. The Windows command prompt can be used to control almost any aspect of a system, with various permission levels required for different subsets of commands. The command prompt can be invoked remotely via Remote Services such as SSH.
Batch files (ex: .bat or .cmd) also provide the shell with a list of sequential commands to run, as well as normal scripting operations such as conditionals and loops. Common uses of batch files include long or repetitive tasks, or the need to run the same set of commands on multiple systems.
Adversaries may leverage cmd to execute various commands and payloads. Common uses include cmd to execute a single command, or abusing cmd interactively with input and output forwarded over a command and control channel.
Execution Prevention
Use application control where appropriate.
Monitoring the following activities in your Organization can help you detect this technique.
Command: Command Execution
Invoking a computer program directive to perform a specific task (ex: Windows EID 4688 of cmd.exe showing command-line parameters, ~/.bash_history, or ~/.zsh_history)
Monitor executed commands and arguments that may abuse the Windows command shell for execution. Usage of the Windows command shell may be common on administrator, developer, or power user systems depending on job function. If scripting is restricted for normal users, then any attempt to enable scripts running on a system would be considered suspicious. If scripts are not commonly used on a system, but enabled, scripts running out of cycle from patching or other administrator functions are suspicious. Scripts should be captured from the file system when possible to determine their actions and intent.
Process: Process Creation
Birth of a new running process (ex: Sysmon EID 1 or Windows EID 4688)
Monitor for newly executed processes that may abuse the Windows command shell for execution.
ABK can extract a malicious Portable Executable (PE) from a photo.
Adversaries may use steganography techniques in order to prevent the detection of hidden information. Steganographic techniques can be used to hide data in digital media such as images, audio tracks, video clips, or text files.
Duqu was an early example of malware that used steganography. It encrypted the gathered information from a victim's system and hid it within an image before exfiltrating the image to a C2 server.
By the end of 2017, a threat group used Invoke-PSImage to hide PowerShell commands in an image file (.png) and execute the code on a victim's system. In this particular case the PowerShell code downloaded another obfuscated script to gather intelligence from the victim's machine and communicate it back to the adversary.
This type of attack technique cannot be easily mitigated with preventive controls since it is based on the abuse of system features.
Monitoring the following activities in your Organization can help you detect this technique.
File: File Metadata
Contextual data about a file, which may include information such as name, the content (ex: signature, headers, or data/media), user/ower, permissions, etc.
Detection of steganography is difficult unless artifacts are left behind by the obfuscation process that are detectable with a known signature. Look for strings or other signatures left in system artifacts related to decoding steganography.
ABK has the ability to inject shellcode into svchost.exe.
Adversaries may inject code into processes in order to evade process-based defenses as well as possibly elevate privileges. Process injection is a method of executing arbitrary code in the address space of a separate live process. 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 process injection may also evade detection from security products since the execution is masked under a legitimate process.
There are many different ways to inject code into a process, many of which abuse legitimate functionalities. These implementations exist for every major OS but are typically platform specific.
More sophisticated samples may perform multiple process injections to segment modules and further evade detection, utilizing named pipes or other inter-process communication (IPC) mechanisms as a communication channel.
Behavior Prevention on Endpoint
Some endpoint security solutions can be configured to block some types of process injection based on common sequences of behavior that occur during the injection process. For example, on Windows 10, Attack Surface Reduction (ASR) rules may prevent Office applications from code injection.
Privileged Account Management
Utilize Yama (ex: /proc/sys/kernel/yama/ptrace_scope) to mitigate ptrace based process injection by restricting the use of ptrace to privileged users only. Other mitigation controls involve the deployment of security kernel modules that provide advanced access control and process restrictions such as SELinux, grsecurity, and AppArmor.
Monitoring the following activities in your Organization can help you detect this technique.
File: File Metadata
Contextual data about a file, which may include information such as name, the content (ex: signature, headers, or data/media), user/ower, permissions, etc.
Monitor for contextual data about a file, which may include information such as name, the content (ex: signature, headers, or data/media), user/ower, permissions, etc.
File: File Modification
Changes made to a file, or its access permissions and attributes, typically to alter the contents of the targeted file (ex: Windows EID 4670 or Sysmon EID 2)
Monitor for changes made to files that may inject code into processes in order to evade process-based defenses as well as possibly elevate privileges.
Module: Module Load
Attaching a module into the memory of a process/program, typically to access shared resources/features provided by the module (ex: Sysmon EID 7)
Monitor DLL/PE file events, specifically creation of these binary files as well as the loading of DLLs into processes. Look for DLLs that are not recognized or not normally loaded into a process.
Process: OS API Execution
Initial construction of a WMI object, such as a filter, consumer, subscription, binding, or provider (ex: Sysmon EIDs 19-21)
Monitoring Windows API calls indicative of the various types of code injection may generate a significant amount of data and may not be directly useful for defense unless collected under specific circumstances for known bad sequences of calls, since benign use of API functions may be common and difficult to distinguish from malicious behavior. Windows API calls such as CreateRemoteThread, SuspendThread/SetThreadContext/ResumeThread, QueueUserAPC/NtQueueApcThread, and those that can be used to modify memory within another process, such as VirtualAllocEx/WriteProcessMemory, may be used for this technique. Monitoring for Linux specific calls such as the ptrace system call should not generate large amounts of data due to their specialized nature, and can be a very effective method to detect some of the common process injection methods.
Process: Process Access
Opening of a process by another process, typically to read memory of the target process (ex: Sysmon EID 10)
Monitor for processes being viewed that may inject code into processes in order to evade process-based defenses as well as possibly elevate privileges.
Process: Process Modification
Changes made to a process, or its contents, typically to write and/or execute code in the memory of the target process (ex: Sysmon EID 8)
Monitor for changes made to processes that may inject code into processes in order to evade process-based defenses as well as possibly elevate privileges.
ABK has the ability to decrypt AES encrypted payloads.
Adversaries may use Obfuscated Files or Information to hide artifacts of an intrusion from analysis. They may require separate mechanisms to decode or deobfuscate that information depending on how they intend to use it. Methods for doing that include built-in functionality of malware or by using utilities present on the system.
One such example is use of certutil to decode a remote access tool portable executable file that has been hidden inside a certificate file. Another example is using the Windows copy /b command to reassemble binary fragments into a malicious payload.
Sometimes a user's action may be required to open it for deobfuscation or decryption as part of User Execution. The user may also be required to input a password to open a password protected compressed/encrypted file that was provided by the adversary.
This type of attack technique cannot be easily mitigated with preventive controls since it is based on the abuse of system features.
Monitoring the following activities in your Organization can help you detect this technique.
File: File Modification
Changes made to a file, or its access permissions and attributes, typically to alter the contents of the targeted file (ex: Windows EID 4670 or Sysmon EID 2)
Monitor for changes made to files for unexpected modifications that attempt to hide artifacts.
Process: Process Creation
Birth of a new running process (ex: Sysmon EID 1 or Windows EID 4688)
Monitor for newly executed processes that attempt to hide artifacts of an intrusion, such as common archive file applications and extensions (ex: Zip and RAR archive tools), and correlate with other suspicious behavior to reduce false positives from normal user and administrator behavior.
Script: Script Execution
Launching a list of commands through a script file (ex: Windows EID 4104)
Monitor for any attempts to enable scripts running on a system would be considered suspicious. If scripts are not commonly used on a system, but enabled, scripts running out of cycle from patching or other administrator functions are suspicious. Scripts should be captured from the file system when possible to determine their actions and intent.
ABK has the ability to identify the installed anti-virus product on the compromised host.
Adversaries may attempt to get a listing of security software, configurations, defensive tools, and sensors that are installed on a system or in a cloud environment. This may include things such as firewall rules and anti-virus. Adversaries may use the information from Security Software Discovery during automated discovery to shape follow-on behaviors, including whether or not the adversary fully infects the target and/or attempts specific actions.
Example 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. It is becoming more common to see macOS malware perform checks for LittleSnitch and KnockKnock software.
Adversaries may also utilize cloud APIs to discover the configurations of firewall rules within an environment. For example, the permitted IP ranges, ports or user accounts for the inbound/outbound rules of security groups, virtual firewalls established within AWS for EC2 and/or VPC instances, can be revealed by the DescribeSecurityGroups action with various request parameters.
This type of attack technique cannot be easily mitigated with preventive controls since it is based on the abuse of system features.
Monitoring the following activities in your Organization can help you detect this technique.
Command: Command Execution
Invoking a computer program directive to perform a specific task (ex: Windows EID 4688 of cmd.exe showing command-line parameters, ~/.bash_history, or ~/.zsh_history)
Monitor executed commands and arguments that may attempt to get a listing of security software, configurations, defensive tools, and sensors that are installed on a system or in a cloud environment.
Firewall: Firewall Enumeration
An extracted list of available firewalls and/or their associated settings/rules (ex: Azure Network Firewall CLI Show commands)
Monitor for an extracted list of available firewalls and/or their associated settings/rules (ex: Azure Network Firewall CLI Show commands)
Firewall: Firewall Metadata
Contextual data about a firewall and activity around it such as name, policy, or status
Monitor for contextual data about a firewall and activity around it such as name, policy, or status
Process: OS API Execution
Initial construction of a WMI object, such as a filter, consumer, subscription, binding, or provider (ex: Sysmon EIDs 19-21)
Monitor for API calls that may attempt to get a listing of security software, configurations, defensive tools, and sensors that are installed on a system or in a cloud environment.
Process: Process Creation
Birth of a new running process (ex: Sysmon EID 1 or Windows EID 4688)
Monitor newly executed processes that may attempt to get a listing of security software, configurations, defensive tools, and sensors that are installed on a system or in a cloud environment.
ABK has the ability to use HTTP in communications with C2.
Adversaries may communicate using application layer protocols associated with web traffic 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.
Protocols such as HTTP and HTTPS that carry web traffic may be very common in environments. HTTP/S packets have many fields and headers in which data can be concealed. An adversary may abuse these protocols to communicate with systems under their control within a victim network while also mimicking normal, expected traffic.
Network Intrusion Prevention
Network intrusion detection and prevention systems that use network signatures to identify traffic for specific adversary malware can be used to mitigate activity at the network level.
Monitoring the following activities in your Organization can help you detect this technique.
Network Traffic: Network Traffic Content
Logged network traffic data showing both protocol header and body values (ex: PCAP)
Monitor and analyze traffic patterns and packet inspection associated to protocol(s), leveraging SSL/TLS inspection for encrypted traffic, that do not follow the expected protocol standards and traffic flows (e.g extraneous packets that do not belong to established flows, gratuitous or anomalous traffic patterns, anomalous syntax, or structure). Consider correlation with process monitoring and command line to detect anomalous processes execution and command line arguments associated to traffic patterns (e.g. monitor anomalies in use of files that do not normally initiate connections for respective protocol(s)).
Network Traffic: Network Traffic Flow
Summarized network packet data, with metrics, such as protocol headers and volume (ex: Netflow or Zeek http.log)
Monitor for web traffic to/from known-bad or suspicious domains and analyze traffic flows that do not follow the expected protocol standards and traffic flows (e.g extraneous packets that do not belong to established flows, or gratuitous or anomalous traffic patterns). Consider correlation with process monitoring and command line to detect anomalous processes execution and command line arguments associated to traffic patterns (e.g. monitor anomalies in use of files that do not normally initiate connections for respective protocol(s)).
ABK has the ability to download files from C2.
Adversaries may transfer tools or other files from an external system into a compromised environment. Tools or files may be copied from an external adversary-controlled system to the victim network through the command and control channel or through alternate protocols such as ftp. Once present, adversaries may also transfer/spread tools between victim devices within a compromised environment (i.e. Lateral Tool Transfer).
Files can also be transferred using various Web Services as well as native or otherwise present tools on the victim system.
On Windows, adversaries may use various utilities to download tools, such as copy, finger, and PowerShell commands such as IEX(New-Object Net.WebClient).downloadString() and Invoke-WebRequest. On Linux and macOS systems, a variety of utilities also exist, such as curl, scp, sftp, tftp, rsync, finger, and wget.
Network Intrusion Prevention
Network intrusion detection and prevention systems that use network signatures to identify traffic for specific adversary malware or unusual data transfer over known protocols like FTP can be used to mitigate activity at the network level. Signatures are often for unique indicators within protocols and may be based on the specific obfuscation technique used by a particular adversary or tool, and will likely be different across various malware families and versions. Adversaries will likely change tool C2 signatures over time or construct protocols in such a way as to avoid detection by common defensive tools.
Monitoring the following activities in your Organization can help you detect this technique.
File: File Creation
Initial construction of a new file (ex: Sysmon EID 11)
Monitor for file creation and files transferred into the network
Network Traffic: Network Connection Creation
Initial construction of a WMI object, such as a filter, consumer, subscription, binding, or provider (ex: Sysmon EIDs 19-21)
Monitor for newly constructed network connections that are sent or received by untrusted hosts or creating files on-system may be suspicious. Use of utilities, such as FTP, that does not normally occur may also be suspicious.
Network Traffic: Network Traffic Content
Logged network traffic data showing both protocol header and body values (ex: PCAP)
Monitor network traffic content for files and other potentially malicious content, especially data coming in from abnormal/unknown domain and IPs.
Network Traffic: Network Traffic Flow
Summarized network packet data, with metrics, such as protocol headers and volume (ex: Netflow or Zeek http.log)
Monitor network data for uncommon data flows (e.g., a client sending significantly more data than it receives from a server). Processes utilizing the network that do not normally have network communication or have never been seen before are suspicious.
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