Analytics Story: IIS Components

Description

Adversaries may install malicious components that run on Internet Information Services (IIS) web servers to establish persistence.

Why it matters

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. 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. 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. (reference MITRE)

Detections

Data Sources

Name ▲▼	Platform ▲▼	Sourcetype ▲▼	Source ▲▼
CrowdStrike ProcessRollup2	N/A	crowdstrike:events:sensor	crowdstrike
Powershell Installed IIS Modules	Windows	Pwsh:InstalledIISModules	powershell://AppCmdModules
Powershell Script Block Logging 4104	Windows	xmlwineventlog	XmlWinEventLog:Microsoft-Windows-PowerShell/Operational
Sysmon EventID 1	Windows	xmlwineventlog	XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
Windows Event Log Application 2282	Windows	XmlWinEventLog	XmlWinEventLog:Application
Windows Event Log Security 4688	Windows	xmlwineventlog	XmlWinEventLog:Security
Windows IIS 29	Windows	IIS:Configuration:Operational	IIS:Configuration:Operational

References

• https://www.microsoft.com/en-us/security/blog/2022/12/12/iis-modules-the-evolution-of-web-shells-and-how-to-detect-them/
• https://attack.mitre.org/techniques/T1505/004/
• https://www.crowdstrike.com/wp-content/uploads/2022/05/crowdstrike-iceapple-a-novel-internet-information-services-post-exploitation-framework-1.pdf
• https://unit42.paloaltonetworks.com/unit42-oilrig-uses-rgdoor-iis-backdoor-targets-middle-east/
• https://www.secureworks.com/research/bronze-union
• https://strontic.github.io/xcyclopedia/library/appcmd.exe-055B2B09409F980BF9B5A3969D01E5B2.html

Source: GitHub | Version: 1