Detects RCE indicators related to the proof-of-concept code for the React Server Remote Code Execution Vulnerability (CV

Hunt Hypothesis

This hunt hypothesis targets adversaries attempting to exploit the React Server Remote Code Execution vulnerability (CVE-2025-55182) by executing malicious payloads through proof-of-concept code within browser extensions or server environments. The SOC team should proactively hunt for these indicators in Azure Sentinel to identify early-stage compromise attempts before attackers can establish persistence or escalate privileges on critical web infrastructure.

YARA Rule

rule EXPL_SUSP_JS_POC_RSC_Detector_Payloads_Dec25 {
   meta:
      description = "Detects RCE indicators related to the proof-of-concept code for the React Server Remote Code Execution Vulnerability (CVE-2025-55182) as used in the RSC Detector browser extension but could be used in other JavaScript based PoC code as well"
      author = "Florian Roth"
      reference = "https://github.com/mrknow001/RSC_Detector"
      date = "2025-12-06"
      score = 70
      id = "98887e97-2dd4-5777-9fab-02805035de14"
   strings:
      $s1 = "process.mainModule.require('child_process').execSync("
      $s2 = ").toString('base64');"

      // harmless test cases - we only want to match real command execution attempts
      $f1 = "echo vulnerability_test"
   condition:
      all of ($s*)
      and not 1 of ($f*)
}

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 3 string patterns in its detection logic.

References

• https://github.com/mrknow001/RSC_Detector
• Source Rule

False Positive Guidance

Here are 3-5 specific false positive scenarios for the React Server Remote Code Execution Vulnerability (CVE-2025-55182) detection rule, tailored for a legitimate enterprise environment:

• Automated CI/CD Pipeline Artifact Scanning

  • Scenario: The organization’s DevOps team uses GitHub Actions or Jenkins to run nightly security scans on the react-server repository. During these builds, the pipeline executes the official RSC Detector proof-of-concept script against a staging environment to validate the vulnerability fix before deployment. This execution triggers the rule as it mimics an active exploitation attempt.
  • Filter/Exclusion: Create an exclusion for process names matching node or npm running under the service account svc-cicd-runner. Additionally, filter out events where the source IP belongs to the internal CI subnet (e.g., 10.20.45.0/24) and the user agent contains GitHub-Hookshot or Jenkins-Agent.

• Scheduled Browser Extension Health Checks

  • Scenario: The enterprise IT department has deployed the RSC Detector browser extension to all 5,000+ workstations for continuous monitoring. A scheduled task runs every morning at 08:00 UTC where the extension’s background service performs a “self-verification” probe against the internal React Server API endpoint. This routine health check executes the PoC code logic, generating RCE indicators that look like external attacks.
  • Filter/Exclusion: Exclude events occurring between 07:45 and 08:15 UTC where the source process is chrome.exe (or msedge.exe) with a specific extension ID (e.g., rsc-detector-ext-v2). Filter based on the destination port being the internal API port (e