Joinersignfrompinch250320072010

Hunt Hypothesis

This YARA rule targets specific binary signatures associated with the “Joinersignfrompinch” artifact, potentially indicating the presence of a low-severity implant or custom tooling used for initial access or lateral movement. Proactively hunting for this signature in Azure Sentinel allows the SOC team to identify dormant or stealthy threats that may not yet trigger high-fidelity alerts, ensuring early detection of subtle adversary footholds within the environment.

YARA Rule

rule Joinersignfrompinch250320072010
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 81 EC 04 01 00 00 8B F4 68 04 01 00 00 56 6A 00 E8 7C 01 00 00 33 C0 6A 00 68 80 00 00 00 6A 03 6A 00 6A 00 68 00 00 00 80 56 E8 50 01 00 00 8B D8 6A 00 6A 00 6A 00 6A 02 6A 00 53 E8 44 01 }

condition:
		$a0 at pe.entry_point
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: A developer or DevOps engineer uses a custom Python or PowerShell script to parse and join log files or CSV data for a specific report, where the script contains string literals or variable names matching the YARA pattern (e.g., joiner, sign, pinch, or specific date strings like 25032007).

  • Filter/Exclusion: Exclude processes initiated by python.exe, python3.exe, or pwsh.exe when the parent process is a known IDE (e.g., code.exe, idea64.exe) or a build tool (e.g., msbuild.exe, gradle). Alternatively, exclude files located in standard development directories like C:\Users\<user>\Projects\ or C:\dev\.

• Scenario: An automated scheduled task (e.g., via Windows Task Scheduler or cron on Linux) runs a data aggregation job that uses a utility like jq, awk, or a custom binary to join JSON/CSV records. The binary or script may contain the specific signature string due to versioning, naming conventions, or embedded metadata.

  • Filter/Exclusion: Exclude processes where the parent is svchost.exe (for Task Scheduler) or systemd/cron (on Linux), and the working directory is under C:\ProgramData\ or /var/spool/cron/. Additionally, whitelist known data processing tools like jq.exe, awk, or sed if they are the direct executors.

• Scenario: A third-party backup or archiving tool (e.g., Veeam, Commvault, or Acronis) creates a temporary file or log entry during a backup job that includes a timestamp or job ID matching the YARA pattern (e.g., `25032007