CVE-2024-39894
📋 TL;DR
This vulnerability in OpenSSH allows attackers to perform timing attacks against password entry when echo is disabled (e.g., during su or sudo operations). The flaw in ObscureKeystrokeTiming logic could enable attackers to infer keystroke timing patterns and potentially guess passwords. It affects systems running OpenSSH 9.5 through 9.7.
💻 Affected Systems
- OpenSSH
⚠️ 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
Attackers could potentially deduce password characters through timing analysis, leading to privilege escalation or unauthorized access to sensitive systems.
Likely Case
Limited password information leakage in controlled environments where attackers can measure precise timing of keystrokes during authentication.
If Mitigated
Minimal impact with strong passwords, network segmentation, and proper access controls limiting attacker proximity.
🎯 Exploit Status
Exploitation requires precise timing measurements and multiple authentication attempts. Public research and proof-of-concept demonstrations exist.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: OpenSSH 9.8
Vendor Advisory: http://www.openwall.com/lists/oss-security/2024/07/03/6
Restart Required: Yes
Instructions:
1. Update OpenSSH to version 9.8 or later. 2. For package managers: 'sudo apt update && sudo apt upgrade openssh-server' (Debian/Ubuntu) or 'sudo yum update openssh' (RHEL/CentOS). 3. Restart SSH service: 'sudo systemctl restart sshd'.
🔧 Temporary Workarounds
Disable password authentication
linuxUse SSH keys instead of passwords for authentication to bypass vulnerable password entry mechanism.
Edit /etc/ssh/sshd_config and set: PasswordAuthentication no
Then restart SSH: sudo systemctl restart sshd
Limit authentication attempts
linuxReduce the number of allowed authentication attempts to limit timing attack opportunities.
Edit /etc/ssh/sshd_config and set: MaxAuthTries 3
Then restart SSH: sudo systemctl restart sshd
🧯 If You Can't Patch
- Implement network segmentation to limit who can attempt SSH authentication
- Use multi-factor authentication to add additional security layer beyond passwords
🔍 How to Verify
Check if Vulnerable:
Check OpenSSH version with: ssh -V 2>&1 | grep -o 'OpenSSH_[0-9.]*' | cut -d_ -f2Check Version:
ssh -VVerify Fix Applied:
Verify version is 9.8 or higher: ssh -V 2>&1 | grep -q 'OpenSSH_9\.[8-9]\|OpenSSH_[1-9][0-9]' && echo 'Patched' || echo 'Vulnerable'📡 Detection & Monitoring
Log Indicators:
- Multiple failed authentication attempts with precise timing patterns
- Unusual authentication timing from single source
Network Indicators:
- High volume of SSH authentication attempts with consistent timing intervals
SIEM Query:
source="sshd" AND "Failed password" | stats count by src_ip | where count > 10🔗 References
- http://www.openwall.com/lists/oss-security/2024/07/03/6
- http://www.openwall.com/lists/oss-security/2024/07/23/4
- http://www.openwall.com/lists/oss-security/2024/07/23/6
- http://www.openwall.com/lists/oss-security/2024/07/28/3
- https://crzphil.github.io/posts/ssh-obfuscation-bypass/
- https://lists.mindrot.org/pipermail/openssh-unix-announce/2024-July/000158.html
- https://news.ycombinator.com/item?id=41508530
- https://security.netapp.com/advisory/ntap-20240712-0004/
- https://www.openssh.com/txt/release-9.8
- https://www.openwall.com/lists/oss-security/2024/07/02/1
- http://seclists.org/fulldisclosure/2024/Sep/33
- http://www.openwall.com/lists/oss-security/2024/07/03/6
- http://www.openwall.com/lists/oss-security/2024/07/23/4
- http://www.openwall.com/lists/oss-security/2024/07/23/6
- http://www.openwall.com/lists/oss-security/2024/07/28/3
- https://lists.mindrot.org/pipermail/openssh-unix-announce/2024-July/000158.html
- https://security.netapp.com/advisory/ntap-20240712-0004/
- https://www.freebsd.org/security/advisories/FreeBSD-SA-25:01.openssh.asc
- https://www.openssh.com/txt/release-9.8
- https://www.openwall.com/lists/oss-security/2024/07/02/1
