The MemStub32 rule detects potential in-memory execution of malicious payloads by identifying suspicious memory stubs commonly used in advanced persistent threats. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify early-stage adversaries leveraging in-memory techniques to evade traditional detection mechanisms.
YARA Rule
rule MemStub32 {
meta:
author = "Jaume Martin"
condition:
hash.md5(0, filesize) == "8987652f26732607b769247adb4e9cce"
}This YARA rule can be deployed in the following contexts:
Scenario: A legitimate system update or patching tool (e.g., Windows Update, Microsoft Endpoint Manager) is running in memory and matches the MemStub32 YARA signature.
Filter/Exclusion: Check for process names like wuauclt.exe, msiexec.exe, or setup.exe using the process.name field.
Scenario: A scheduled administrative task (e.g., Task Scheduler) is executing a legitimate script or executable that is flagged by the MemStub32 rule.
Filter/Exclusion: Filter by process.name for known administrative tools like schtasks.exe or taskhost.exe.
Scenario: A legitimate third-party application (e.g., 7-Zip, WinRAR, or Notepad++) is loaded into memory and matches the MemStub32 signature.
Filter/Exclusion: Use process.name to exclude known benign applications such as 7z.exe, rar.exe, or notepad++.exe.
Scenario: A memory dump or forensic tool (e.g., ProcDump, Volatility) is being used by an administrator for troubleshooting and is flagged by the rule.
Filter/Exclusion: Filter by process.name for tools like procdump.exe or vol.py.
Scenario: A legitimate system service (e.g., Windows Event Log service, Task Scheduler service) is using memory injection techniques for legitimate operations.
Filter/Exclusion: Use process.name to exclude known system services like eventlog.exe or svchost.exe.