Angler Exploit Kit Detection

Hunt Hypothesis

The Angler Exploit Kit Detection identifies potential exploitation attempts by malicious actors leveraging outdated or vulnerable software to deliver payloads. SOC teams should proactively hunt for this behavior in Azure Sentinel to detect and mitigate early-stage compromise attempts that may evade traditional detection methods.

YARA Rule

rule angler_flash4 : EK
{
meta:
   author = "Josh Berry"
   date = "2016-06-26"
   description = "Angler Exploit Kit Detection"
   hash0 = "dbb3f5e90c05602d92e5d6e12f8c1421"
   sample_filetype = "unknown"
   yaragenerator = "https://github.com/Xen0ph0n/YaraGenerator"
strings:
   $string0 = "_u;cwD;"
   $string1 = "lhNp74"
   $string2 = "Y0GQ%v"
   $string3 = "qjqCb,nx"
   $string4 = "vn{l{Wl"
   $string5 = "5j5jz5"
   $string6 = "a3EWwhM"
   $string7 = "hVJb/4Aut"
   $string8 = ",lm4v,"
   $string9 = ",6MekS"
   $string10 = "YM.mxzO"
   $string11 = ";6 -$E"
   $string12 = "QA%: fy"
   $string13 = "<@{qvR"
   $string14 = "b9'$'6l"
   $string15 = ",x:pQ@-"
   $string16 = "2Dyyr9"
condition:
   16 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 17 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: Scheduled System Maintenance Task
  Description: A legitimate scheduled task runs a script that mimics exploit kit behavior, such as downloading a payload or executing a script.
  Filter/Exclusion: Exclude tasks associated with schtasks.exe or Task Scheduler with known maintenance scripts (e.g., C:\Windows\System32\wbem\Microsoft.WbemTest.exe).

• Scenario: Admin Performing Remote Code Execution (RCE) via PowerShell
  Description: An administrator uses PowerShell to execute a script that resembles exploit kit behavior, such as downloading a payload or modifying system settings.
  Filter/Exclusion: Exclude PowerShell scripts executed by users with administrative privileges and signed by trusted sources (e.g., PSReadLine or Microsoft.PowerShell modules).

• Scenario: Software Update or Patch Deployment
  Description: A legitimate software update or patch deployment process includes downloading and executing a script that triggers the rule.
  Filter/Exclusion: Exclude processes related to patch management tools like Microsoft Update, WSUS, or SCCM (e.g., C:\Windows\System32\wusa.exe).

• Scenario: Security Tool or EDR Agent Behavior
  Description: A security tool or endpoint detection and response (EDR) agent performs actions that resemble exploit kit behavior, such as downloading payloads or modifying system configurations.
  Filter/Exclusion: Exclude processes from known security tools like Microsoft Defender, CrowdStrike, or SentinelOne (e.g., C:\Windows\System32\mpcmdrun.exe).

• Scenario: Internal Development or Testing Environment
  Description: A developer or tester runs a script or tool that mimics exploit kit behavior as part of internal testing or development.
  Filter/Exclusion: Exclude processes running from development directories or