CVE-2025-29927 PoC — Authorization Bypass in Next.js Middleware

Source

Associated Vulnerability

Description

Sigma Rule for CVE-2025–29927 Detection

Readme

# CVE-2025-29927 Report

## Overview
CVE-2025-29927 is a security vulnerability in Next.js middleware, allowing attackers to bypass authentication by modifying specific HTTP headers.

## Exploitation
Attackers can send a request with the header `x-middleware-subrequest: middleware` to bypass authentication.

## Detection
Detection strategies include:
- Monitoring HTTP headers for suspicious `x-middleware-subrequest` values.
- Implementing Sigma rules to detect unauthorized requests.
- Enabling logging for middleware actions in Next.js applications.

## Mitigation
- Update to the latest patched version of Next.js.
- Implement strict request header validation.
- Enforce authentication at the API layer instead of relying solely on middleware.

## References
- [CVE Details](https://nvd.nist.gov/vuln/detail/CVE-2025-29927)

Can We Use a Sigma Rule to Detect CVE-2025-29927?
✅ Yes, but only if the logging environment captures HTTP headers correctly. If the web server (e.g., Apache, Nginx) logs the x-middleware-subrequest header, the Sigma rule will successfully detect the attack.

🚨 No, if the logs do not contain this header. If the web server does not record HTTP headers in the logs, the Sigma rule will not detect the exploitation, even if the rule is correctly written.

📌 Recommendation: Ensure that your logging configuration includes full HTTP headers before relying on Sigma rules for detection.

File Snapshot

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├── [1.4K]  README.md
└── [ 646]  sigma_rule.yml

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