CVE-2026-3731
📋 TL;DR
CVE-2026-3731 is an out-of-bounds read vulnerability in libssh's SFTP extension handler that allows remote attackers to read memory beyond allocated buffers. This affects libssh versions up to 0.11.3. Systems using vulnerable libssh versions for SSH/SFTP services are at risk.
💻 Affected Systems
- libssh
⚠️ 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 information disclosure leading to memory content leakage, potentially exposing sensitive data or enabling further exploitation.
Likely Case
Application crash or denial of service due to invalid memory access, with possible limited information disclosure.
If Mitigated
No impact if proper input validation or memory protections are in place, or if vulnerable functions aren't used.
🎯 Exploit Status
Remote exploitation requires sending specially crafted SFTP extension requests. No public exploit code is currently known.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 0.11.4 or 0.12.0
Vendor Advisory: https://www.libssh.org/security/
Restart Required: Yes
Instructions:
1. Download libssh 0.11.4 or 0.12.0 from libssh.org
2. Compile and install the new version
3. Restart all services using libssh
4. Recompile any applications statically linked to libssh
🔧 Temporary Workarounds
Disable SFTP extensions
allIf SFTP extensions are not required, disable them to prevent exploitation
Configure SSH/SFTP server to not use libssh's SFTP extension functionality
🧯 If You Can't Patch
- Implement network segmentation to restrict access to vulnerable systems
- Deploy intrusion detection systems to monitor for exploitation attempts
🔍 How to Verify
Check if Vulnerable:
Check libssh version: ldd --version | grep libssh or check package managerCheck Version:
ssh -V 2>&1 | grep libssh || ldd $(which ssh) | grep libsshVerify Fix Applied:
Verify installed libssh version is 0.11.4 or higher📡 Detection & Monitoring
Log Indicators:
- Unexpected application crashes
- Memory access violation errors in system logs
Network Indicators:
- Unusual SFTP extension requests
- Multiple failed SFTP connections
SIEM Query:
source="ssh.log" AND ("segmentation fault" OR "out of bounds" OR "memory violation")🔗 References
- https://gitlab.com/libssh/libssh-mirror/-/commit/855a0853ad3abd4a6cd85ce06fce6d8d4c7a0b60
- https://vuldb.com/?ctiid.349709
- https://vuldb.com/?id.349709
- https://vuldb.com/?submit.767120
- https://www.libssh.org/files/0.12/libssh-0.12.0.tar.xz
- https://www.libssh.org/security/advisories/libssh-2026-sftp-extensions.txt
