possible exploit

Hunt Hypothesis

The ‘possible_exploit’ rule detects potential malicious code or exploit artifacts that may indicate advanced threat activity. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate early-stage exploitation attempts before they escalate.

YARA Rule

rule possible_exploit : PDF raw
{
	meta:
		author = "Glenn Edwards (@hiddenillusion)"
		version = "0.1"
		weight = 3
		
	strings:
		$magic = { 25 50 44 46 }
		
		$attrib0 = /\/JavaScript /
		$attrib3 = /\/ASCIIHexDecode/
		$attrib4 = /\/ASCII85Decode/

		$action0 = /\/Action/
		$action1 = "Array"
		$shell = "A"
		$cond0 = "unescape"
		$cond1 = "String.fromCharCode"
		
		$nop = "%u9090%u9090"
	condition:
		$magic in (0..1024) and (2 of ($attrib*)) or ($action0 and #shell > 10 and 1 of ($cond*)) or ($action1 and $cond0 and $nop)
}

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 10 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: Legitimate scheduled job using a known exploit framework
  Example: A scheduled job runs msfvenom to generate a payload for a penetration test.
  Filter/Exclusion: Exclude processes initiated by a known test environment or user with “penetration testing” in their AD group.

• Scenario: Admin task involving exploit-related tools
  Example: An admin uses Metasploit to test a patch’s effectiveness against a known vulnerability.
  Filter/Exclusion: Exclude processes initiated by users with “security_admin” or “red_team” roles in the SIEM or AD.

• Scenario: Email gateway scanning with exploit detection
  Example: An email gateway scans a legitimate attachment containing a known exploit signature (e.g., CVE-2023-1234).
  Filter/Exclusion: Exclude files with known signatures from internal security tools or whitelisted vendors.

• Scenario: File share monitoring with benign exploit artifacts
  Example: A file share contains a script with a CVE-2023-5678 exploit signature used for internal security research.
  Filter/Exclusion: Exclude files located in a dedicated research directory or marked with a “security_research” tag.

• Scenario: Endpoint EDR scanning of legitimate exploit tools
  Example: An EDR tool scans a system where Cobalt Strike is used for internal red team exercises.
  Filter/Exclusion: Exclude processes initiated by users with “red_team” or “internal_security” in their user profile.