PESpinv1304Cyberbob

Hunt Hypothesis

This YARA rule targets specific characteristics of the Cyberbob malware family, indicating the presence of a known threat actor’s tooling on a host. Proactively hunting for this signature allows the SOC to identify compromised endpoints early, enabling rapid containment before the malware can establish persistence or execute its payload.

YARA Rule

rule PESpinv1304Cyberbob
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB 01 68 60 E8 00 00 00 00 8B 1C 24 83 C3 12 81 2B E8 B1 06 00 FE 4B FD 82 2C 24 88 DF 46 00 0B E4 74 9E 75 01 C7 81 73 04 D7 7A F7 2F 81 73 19 77 00 43 B7 F6 C3 6B B7 00 00 F9 FF E3 C9 C2 08 00 A3 68 72 01 FF 5D 33 C9 41 E2 17 EB 07 EA EB 01 EB EB 0D FF }

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 Ghidra or IDA Pro to perform static analysis on a proprietary internal application binary. These tools often load the PE file into memory for disassembly, which can trigger YARA rules looking for specific section headers or import tables associated with “Cyberbob” (a known malware family often using obfuscated sections).

  • Filter/Exclusion: Exclude processes where the parent process is ghidra_run.exe, ida.exe, or idaw.exe, or exclude files located in specific development directories like C:\Projects\ or D:\Analysis\ if the rule is file-based.

• Scenario: An IT administrator runs Sysinternals Suite tools (specifically strings.exe or dump.exe) to inspect a corrupted or suspicious executable during troubleshooting. The act of dumping or parsing the PE structure can cause the file to be re-serialized or loaded in a way that matches the YARA pattern, especially if the tool creates a temporary copy in %TEMP%.

  • Filter/Exclusion: Exclude events where the file path contains \Sysinternals\ or where the parent process is strings.exe, dump.exe, or procexp.exe.

• Scenario: A scheduled maintenance job runs 7-Zip (7z.exe) to compress or extract a large archive of legacy application binaries. During the extraction process, 7-Zip may temporarily write PE files to disk in a staging area. If the YARA rule scans files in real-time or via a file watcher, these transient files might match the pattern before being moved to their final location.

  • Filter/Exclusion: Exclude files with paths containing \7z\ or \Archive\ or exclude processes where the parent is 7z.exe or 7zG.exe.

• **Scenario