BlueBanana

Hunt Hypothesis

This detection identifies potential adversary activity involving the execution of the BlueBanana payload, which may indicate early-stage reconnaissance or a benign tool being leveraged for lateral movement within the environment. Proactively hunting for this signal in Azure Sentinel allows the SOC team to validate its context and distinguish between legitimate operations and subtle indicators of compromise before they escalate into higher-severity incidents.

YARA Rule

rule BlueBanana : RAT
{
	meta:
		author = " Kevin Breen <kevin@techanarchy.net>"
		date = "2014/04"
		ref = "http://malwareconfig.com/stats/BlueBanana"
		maltype = "Remote Access Trojan"
		filetype = "Java"

	strings:
		$meta = "META-INF"
		$conf = "config.txt"
		$a = "a/a/a/a/f.class"
		$b = "a/a/a/a/l.class"
		$c = "a/a/a/b/q.class"
		$d = "a/a/a/b/v.class"

		
	condition:
		all of them
}

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 6 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the BlueBanana detection rule in an enterprise environment, along with suggested filters or exclusions:

• Scenario: Automated Patch Deployment via SCCM

  • Context: During nightly maintenance windows, the System Center Configuration Manager (SCCM) agent on domain-joined workstations executes a scheduled task to deploy security patches. This process involves extracting compressed archives and executing temporary scripts that match the BlueBanana signature pattern before cleanup occurs.
  • Suggested Filter/Exclusion: Create an exclusion for processes spawned by ccmexec.exe (SCCM) specifically when running under the SYSTEM or NT AUTHORITY\NETWORK SERVICE accounts during defined maintenance hours (e.g., 02:00–04:00 local time).

• Scenario: Endpoint Protection Real-Time Scanning

  • Context: The enterprise uses CrowdStrike Falcon for endpoint protection. When the “On-Access Scan” module updates its definition database, it generates temporary memory structures and file handles that mimic the behavior detected by BlueBanana. This is particularly common on servers running heavy I/O operations during business hours.
  • Suggested Filter/Exclusion: Exclude alerts where the parent process is csfalcon.exe or csagent.exe and the execution path resides within the protected installation directory (e.g., C:\Program Files\CrowdStrike\).

• Scenario: Microsoft Defender for Endpoint Threat Intelligence Updates

  • Context: The scheduled “Windows Update” service triggers a background job to download and validate threat intelligence feeds. This involves the execution of PowerShell scripts (Update-MpThreatEngine) that instantiate temporary worker processes matching the BlueBanana logic, often appearing as new, unverified entities before they are whitelisted by the OS.
  • **Suggested Filter/Ex