Server Software Component: IIS Components
- ID
- T1505.004
- Tactics
- TA0003 Persistence
- Sub-technique of
- T1505 Server Software Component
- Platforms
- Windows
- Data sources
- File Modification, File Creation, Module Load, Process Creation, Application Log Content, Service Modification
- Source
- attack.mitre.org
- MITRE last modified
- 25 Oct 2025
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.[2][3][4][5]
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.[3][2][6][7][5][8]
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.[9][5][10]
Detection
- DET0068 Detection Strategy for T1505.004 - Malicious IIS Components
Data components: File Modification, File Creation, Module Load, Process Creation, Application Log Content, Service Modification
Mitigations (4)
- 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.
- 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.[1]
- M1045 Code Signing
Ensure IIS DLLs and binaries are signed by the correct application developers.
- M1047 Audit
Regularly check installed IIS components to verify the integrity of the web server and identify if unexpected changes have been made.