CVE-2025-23016
📋 TL;DR
CVE-2025-23016 is an integer overflow vulnerability in FastCGI fcgi2 library versions 2.x through 2.4.4 that leads to heap-based buffer overflow when processing crafted nameLen or valueLen parameters via IPC socket. This allows remote attackers to execute arbitrary code or cause denial of service. Affected systems include any application using the vulnerable fcgi2 library for FastCGI communication.
💻 Affected Systems
- FastCGI fcgi2 library
- Applications using fcgi2 library
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with the privileges of the FastCGI process, potentially leading to full system compromise.
Likely Case
Denial of service through application crashes or remote code execution in vulnerable configurations.
If Mitigated
Limited impact if proper network segmentation and least privilege principles are applied.
🎯 Exploit Status
Exploitation requires sending crafted data to the IPC socket, which may be accessible remotely depending on configuration.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.4.5
Vendor Advisory: https://github.com/FastCGI-Archives/fcgi2/releases/tag/2.4.5
Restart Required: Yes
Instructions:
1. Download fcgi2 version 2.4.5 or later from official repository. 2. Replace existing fcgi2 installation with patched version. 3. Recompile any applications using fcgi2. 4. Restart affected services.
🔧 Temporary Workarounds
Network Access Restriction
linuxRestrict access to FastCGI IPC sockets using firewall rules or network segmentation.
iptables -A INPUT -p tcp --dport [fcgi_port] -j DROP
iptables -A INPUT -p unix -m socket --socket [fcgi_socket] -j DROP
🧯 If You Can't Patch
- Implement strict network segmentation to isolate FastCGI services from untrusted networks.
- Deploy application-level firewalls or WAF with buffer overflow protection rules.
🔍 How to Verify
Check if Vulnerable:
Check fcgi2 library version: ldd /path/to/application | grep fcgi && strings /usr/lib/libfcgi.so | grep 'fcgi version'Check Version:
strings /usr/lib/libfcgi.so | grep 'fcgi version' || fcgi-versionVerify Fix Applied:
Verify installed fcgi2 version is 2.4.5 or later: fcgi-version or check library file version.📡 Detection & Monitoring
Log Indicators:
- Application crashes with segmentation faults
- Unusual memory allocation patterns in system logs
- Failed FastCGI connection attempts
Network Indicators:
- Unusual traffic to FastCGI ports (typically 9000+)
- Malformed FastCGI packets in network captures
SIEM Query:
source="application.logs" AND ("segmentation fault" OR "buffer overflow" OR "fcgi crash")🔗 References
- https://github.com/FastCGI-Archives/fcgi2/issues/67
- https://github.com/FastCGI-Archives/fcgi2/releases/tag/2.4.5
- https://www.synacktiv.com/en/publications/cve-2025-23016-exploiting-the-fastcgi-library
- http://www.openwall.com/lists/oss-security/2025/04/23/4
- https://lists.debian.org/debian-lts-announce/2025/10/msg00009.html
- https://www.synacktiv.com/en/publications/cve-2025-23016-exploiting-the-fastcgi-library
