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

Hunt Hypothesis

This hunt hypothesis identifies potential Remote Code Execution attacks exploiting React Server vulnerabilities by analyzing proof-of-concept execution patterns that may indicate active exploitation or reconnaissance. Proactively hunting for these indicators in Azure Sentinel is critical to rapidly detect and mitigate high-severity threats before adversaries can establish persistence or execute malicious payloads within JavaScript-based environments.

YARA Rule

rule EXPL_SUSP_JS_POC_Dec25 {
   meta:
      description = "Detects RCE indicators related to the proof-of-concept code for the React Server Remote Code Execution Vulnerability (CVE-2025-55182) but could be used in other JavaScript based PoC code as well"
      author = "Florian Roth"
      reference = "https://github.com/msanft/CVE-2025-55182/blob/main/poc.py"
      date = "2025-12-05"
      modified = "2025-12-06"
      score = 70
      id = "114c83f8-b798-5db9-a054-a6148dde7d5a"
   strings:
      $xr1 = /process\.mainModule\.require\(["']child_process["']\).{5,40}\(["'](whoami|powershell|\/bin\/sh|\/bin\/bash|wget|curl|cat \/etc\/passwd|uname|id["'])/
   condition:
      1 of them
      // not XML
      and not uint16(0) == 0x3c3f
}

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 1 string patterns in its detection logic.

References

False Positive Guidance

Here are 4 specific false positive scenarios for the React Server RCE Vulnerability (CVE-2025-55182) detection rule, including suggested filters and exclusions:

Scenario: Automated Security Scanning by SAST/DAST Tools
- Context: Continuous Integration/Continuous Deployment (CI/CD) pipelines utilizing tools like SonarQube, Checkmarx, or Veracode often execute proof-of-concept (PoC) scripts against the React Server to validate vulnerability coverage. These scanners inject specific JavaScript payloads that mimic the RCE signature defined in the rule, triggering alerts during nightly builds or pre-deployment gates.
- Filter/Exclusion: Create a whitelist exclusion for processes running under the service accounts of these scanning tools (e.g., svc-sonarqube, checkmarx-agent) and restrict the alert to only trigger when the source IP is external to the internal build network range (e.g., exclude 10.20.x.x).
Scenario: Scheduled Maintenance Jobs for Dependency Updates
- Context: DevOps teams utilize scheduled tasks via Ansible, Terraform, or Cron jobs that run a custom JavaScript-based PoC script to verify the integrity of React Server dependencies before applying updates. These scripts often execute the exact same RCE indicator logic as the vulnerability proof-of-concept code, causing recurring alerts during maintenance windows (e.g., every Sunday at 02:00 UTC).
- Filter/Exclusion: Implement a time-based exclusion window (e.g., Sunday 01:30 - 04:00) for the specific host group running these maintenance scripts, or add a filter to suppress alerts where the command line arguments contain keywords like --maintenance-mode or --verify-dependencies.