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A critical vulnerability (CVE-2025-29927) has been identified in Next.js middleware, allowing attackers to bypass security controls. The vulnerability is detected via specific HTTP headers, and a Nuclei template has been released to identify affected systems.
You Should Know:
Detection & Verification
Use the following Nuclei command to scan for vulnerable Next.js instances:
nuclei -t CVE-2025-29927.yaml -u https://target.com
Manual Verification Steps
1. Check Next.js Headers:
curl -I https://target.com | grep -i "x-nextjs|middleware"
If headers like `x-nextjs-page` or `x-middleware` are present, the site may be vulnerable.
2. Exploit Simulation (For Testing Only):
curl -X GET -H "X-Bypass-Middleware: true" https://target.com/protected-route
If the request bypasses middleware restrictions, the vulnerability exists.
3. Mitigation Steps:
- Update Next.js to the latest patched version.
- Implement strict request validation in middleware.
- Use WAF rules to block anomalous headers.
Log Analysis for Attacks
Check server logs for suspicious middleware bypass attempts:
grep -i "x-bypass-middleware|middleware-bypass" /var/log/nginx/access.log
Automated Patching with Linux
Use a cron job to check for Next.js updates:
0 3 * * * /usr/bin/curl -s https://api.github.com/repos/vercel/next.js/releases/latest | grep "tag_name"
What Undercode Say
This vulnerability highlights the risks of middleware misconfigurations in modern web frameworks. Security teams must:
– Regularly audit middleware logic.
– Monitor HTTP headers for anomalies.
– Use automated scanners like Nuclei for continuous testing.
Linux & Windows Commands for Further Analysis:
- Linux:
nmap -sV --script=http-headers target.com tcpdump -i eth0 port 443 -w nextjs_traffic.pcap
- Windows (PowerShell):
Invoke-WebRequest -Uri "https://target.com" -Headers @{"X-Test" = "BypassAttempt"} Get-WinEvent -LogName "Application" | Where-Object { $_.Message -like "*Next.js*" }
Expected Output:
- Detection logs confirming middleware bypass.
- Updated Next.js instances with patched middleware.
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References:
Reported By: Saurabh B294b21aa – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
