Skip to content

T1505.004 IIS Components

Adversaries may install malicious components that run on Internet Information Services (IIS) web servers to establish persistence. IIS provides several mechanisms to extend the functionality of the web servers. For example, Internet Server Application Programming Interface (ISAPI) extensions and filters can be installed to examine and/or modify incoming and outgoing IIS web requests. Extensions and filters are deployed as DLL files that export three functions: Get{Extension/Filter}Version, Http{Extension/Filter}Proc, and (optionally) Terminate{Extension/Filter}. IIS modules may also be installed to extend IIS web servers.8953

Adversaries may install malicious ISAPI extensions and filters to observe and/or modify traffic, execute commands on compromised machines, or proxy command and control traffic. ISAPI extensions and filters may have access to all IIS web requests and responses. For example, an adversary may abuse these mechanisms to modify HTTP responses in order to distribute malicious commands/content to previously comprised hosts.9871310

Adversaries may also install malicious IIS modules to observe and/or modify traffic. IIS 7.0 introduced modules that provide the same unrestricted access to HTTP requests and responses as ISAPI extensions and filters. IIS modules can be written as a DLL that exports RegisterModule, or as a .NET application that interfaces with ASP.NET APIs to access IIS HTTP requests.634

Item Value
ID T1505.004
Sub-techniques T1505.001, T1505.002, T1505.003, T1505.004, T1505.005, T1505.006
Tactics TA0003
Platforms Windows
Version 1.1
Created 03 June 2021
Last Modified 24 October 2025

Procedure Examples

ID Name Description
S1022 IceApple IceApple is an IIS post-exploitation framework, consisting of 18 modules that provide several functionalities.12
C0022 Operation Dream Job During Operation Dream Job, Lazarus Group targeted Windows servers running Internet Information Systems (IIS) to install C2 components.13
S0072 OwaAuth OwaAuth has been loaded onto Exchange servers and disguised as an ISAPI filter (owaauth.dll). The IIS w3wp.exe process then loads the malicious DLL.1
S0258 RGDoor RGDoor establishes persistence on webservers as an IIS module.24
C0058 SharePoint ToolShell Exploitation During SharePoint ToolShell Exploitation, threat actors modified Internet Information Services (IIS) components to load suspicious .NET assemblies for persistence.14

Mitigations

ID Mitigation Description
M1047 Audit Regularly check installed IIS components to verify the integrity of the web server and identify if unexpected changes have been made.
M1045 Code Signing Ensure IIS DLLs and binaries are signed by the correct application developers.
M1038 Execution Prevention Restrict unallowed ISAPI extensions and filters from running by specifying a list of ISAPI extensions and filters that can run on IIS.11
M1026 Privileged Account Management Do not allow administrator accounts that have permissions to add IIS components to be used for day-to-day operations that may expose these permissions to potential adversaries and/or other unprivileged systems.

References

  1. Dell SecureWorks Counter Threat Unit Threat Intelligence. (2015, August 5). Threat Group-3390 Targets Organizations for Cyberespionage. Retrieved August 18, 2018. ↩↩

  2. Falcone, R. (2018, January 25). OilRig uses RGDoor IIS Backdoor on Targets in the Middle East. Retrieved July 6, 2018. ↩

  3. Grunzweig, J. (2013, December 9). The Curious Case of the Malicious IIS Module. Retrieved June 3, 2021. ↩↩↩

  4. Hromcová, Z., Cherepanov, A. (2021). Anatomy of Native IIS Malware. Retrieved September 9, 2021. ↩↩

  5. Julien. (2011, February 2). IIS Backdoor. Retrieved June 3, 2021. ↩

  6. Microsoft. (2007, November 24). IIS Modules Overview. Retrieved June 17, 2021. ↩

  7. Microsoft. (2017, June 16). Intercepting All Incoming IIS Requests. Retrieved June 3, 2021. ↩

  8. Microsoft. (2017, June 16). ISAPI Extension Overview. Retrieved June 3, 2021. ↩↩

  9. Microsoft. (2017, June 16). ISAPI Filter Overview. Retrieved June 3, 2021. ↩↩

  10. MMPC. (2012, October 3). Malware signed with the Adobe code signing certificate. Retrieved June 3, 2021. ↩

  11. Microsoft. (2016, September 26). ISAPI/CGI Restrictions . Retrieved June 3, 2021. ↩

  12. CrowdStrike. (2022, May). ICEAPPLE: A NOVEL INTERNET INFORMATION SERVICES (IIS) POST-EXPLOITATION FRAMEWORK. Retrieved June 27, 2022. ↩

  13. Cashman, M. (2020, July 29). Operation North Star Campaign. Retrieved December 20, 2021. ↩

  14. Microsoft Threat Intelligence. (2025, July 22). Disrupting active exploitation of on-premises SharePoint vulnerabilities. Retrieved October 15, 2025. ↩