Angler Exploit Kit Detection

Hunt Hypothesis

Angler Exploit Kit activity is detected through unusual network traffic patterns and suspicious file execution behavior indicative of exploit kit deployment. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate potential compromise from Angler, which is known for delivering malware via exploit kits.

YARA Rule

rule angler_flash5 : EK
{
meta:
   author = "Josh Berry"
   date = "2016-06-26"
   description = "Angler Exploit Kit Detection"
   hash0 = "9f809272e59ee9ecd71093035b31eec6"
   sample_filetype = "unknown"
   yaragenerator = "https://github.com/Xen0ph0n/YaraGenerator"
strings:
   $string0 = "0k%2{u"
   $string1 = "\\Pb@(R"
   $string2 = "ys)dVI"
   $string3 = "tk4_y["
   $string4 = "LM2Grx"
   $string5 = "n}s5fb"
   $string6 = "jT Nx<hKO"
   $string7 = "5xL>>}"
   $string8 = "S%,1{b"
   $string9 = "C'3g7j"
   $string10 = "}gfoh]"
   $string11 = ",KFVQb"
   $string12 = "LA;{Dx"
condition:
   12 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 13 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: Scheduled System Maintenance Task
  Description: A legitimate system maintenance task, such as Windows Update or disk cleanup, may trigger the rule due to similar network behavior.
  Filter/Exclusion: Exclude traffic originating from known system processes (e.g., svchost.exe, taskhost.exe) or use a filter like process.name != "svchost.exe".

• Scenario: Admin Performing Remote Desktop Protocol (RDP) Session
  Description: An administrator using RDP to access a remote server may trigger the rule if the session involves outbound traffic to a suspicious IP or port.
  Filter/Exclusion: Exclude traffic associated with RDP sessions by checking the process.name for mstsc.exe or using a filter like process.name contains "mstsc".

• Scenario: Legitimate Software Update via Microsoft Endpoint Manager (MEM)
  Description: A software update pushed via Microsoft Endpoint Manager may use similar exploit kit techniques to download payloads, triggering the rule.
  Filter/Exclusion: Exclude traffic from known MEM servers or use a filter like destination.ip in (list of known MEM servers).

• Scenario: User Accessing a Phishing Simulation Site
  Description: A user clicking on a phishing link that redirects to a simulated attack page may trigger the rule due to similar exploit kit behavior.
  Filter/Exclusion: Exclude traffic to known phishing simulation domains (e.g., phishsim.example.com) using a filter like destination.domain == "phishsim.example.com".

• Scenario: Internal Network Scanning by Security Tools
  Description: A security tool like Nessus or Qualys performing internal network scanning may generate traffic that resembles exploit kit activity.
  Filter/Exclusion: Exclude traffic from known security tools by checking the process.name for nessusd, `