Detects error messages caused by the exploitation of the React Server Remote Code Execution Vulnerability (CVE-2025-5518

Hunt Hypothesis

This hunt hypothesis targets adversaries exploiting the React Server Remote Code Execution vulnerability (CVE-2025-5518) in Next.js applications to execute arbitrary code through specific error message patterns. Proactively hunting for these indicators within Azure Sentinel is critical because successful exploitation allows attackers to gain immediate command-line access, potentially leading to full system compromise before standard alerts trigger.

YARA Rule

rule EXPL_RCE_React_Server_Next_JS_CVE_2025_66478_Errors_Dec25 {
   meta:
      description = "Detects error messages caused by the exploitation of the React Server Remote Code Execution Vulnerability (CVE-2025-55182) in Next.js applications (CVE-2025-66478). This can also be caused by vulnerability scanning."
      author = "Florian Roth"
      reference = "https://github.com/Malayke/Next.js-RSC-RCE-Scanner-CVE-2025-66478"
      date = "2025-12-05"
      score = 65
      id = "6baeb522-6299-56a2-be27-21c6b668439b"
   strings:
      $s1 = "[Error: NEXT_REDIRECT]"
      $s2 = "digest: 'uid=0(root) gid=0(root)"
   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 2 string patterns in its detection logic.

References

• https://github.com/Malayke/Next.js-RSC-RCE-Scanner-CVE-2025-66478
• Source Rule

False Positive Guidance

Here are 3-5 specific false positive scenarios for the Detects error messages caused by the exploitation of the React Server Remote Code Execution Vulnerability (CVE-2025-5518) rule, along with suggested filters and exclusions:

• Automated Security Scanning Traffic

  • Scenario: Scheduled vulnerability scanners (e.g., Tenable Nessus, Qualys, or OpenVAS) actively probe the Next.js application endpoints to verify patch levels. These tools often send malformed payloads or specific attack signatures that trigger error messages resembling the CVE-2025-5518 exploitation pattern, even though they are performing legitimate discovery rather than an actual breach.
  • Suggested Filter/Exclusion: Create a rule exclusion based on the Source IP belonging to the internal security scanning subnet (e.g., 10.50.40.0/24) or filter events where the User-Agent header contains known scanner identifiers like “Nessus” or “Qualys”.

• CI/CD Pipeline Integration Tests

  • Scenario: During nightly build cycles, the GitHub Actions or Jenkins pipeline executes automated integration tests against the staging environment. These tests frequently simulate edge-case inputs and error conditions to validate the React Server’s resilience, generating log entries that mimic the specific error signatures of the RCE vulnerability.
  • Suggested Filter/Exclusion: Exclude alerts originating from CI/CD service accounts (e.g., svc-github-actions, jenkins-build) or filter events occurring within the defined maintenance window (e.g., 02:00–04:00 UTC) where these pipelines are active.

• Scheduled Data Migration and Backup Jobs

  • Scenario: Enterprise data management tools like Talend or custom Python scripts running