CVE-2025-5689
📋 TL;DR
This vulnerability in Ubuntu's authd service incorrectly assigns root group membership to first-time SSH users during pre-authentication. This allows unauthorized privilege escalation, affecting Ubuntu systems using authd for SSH authentication.
💻 Affected Systems
- Ubuntu authd
📦 What is this software?
Authd by Canonical
⚠️ Risk & Real-World Impact
Worst Case
An attacker gains root-level access to the system through SSH, enabling complete system compromise, data theft, and lateral movement.
Likely Case
Unauthorized users gain elevated privileges to access sensitive files, modify system configurations, or install malicious software.
If Mitigated
With proper network segmentation and least privilege controls, impact is limited to the affected SSH session and specific services.
🎯 Exploit Status
Exploitation requires valid SSH credentials but no special technical skills.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Ubuntu security advisory for specific version
Vendor Advisory: https://github.com/ubuntu/authd/security/advisories/GHSA-g8qw-mgjx-rwjr
Restart Required: Yes
Instructions:
1. Update system packages: sudo apt update && sudo apt upgrade
2. Specifically update authd package if available separately
3. Restart SSH service: sudo systemctl restart ssh
🔧 Temporary Workarounds
Disable authd for SSH
linuxConfigure SSH to use alternative authentication methods instead of authd
Edit /etc/ssh/sshd_config to remove authd references
Restart SSH: sudo systemctl restart ssh
🧯 If You Can't Patch
- Restrict SSH access to trusted networks only using firewall rules
- Implement multi-factor authentication for SSH access
🔍 How to Verify
Check if Vulnerable:
Check if authd is configured for SSH authentication and test first-time user login group assignmentCheck Version:
dpkg -l | grep authdVerify Fix Applied:
Verify authd package version is updated and test that first-time users no longer get root group membership📡 Detection & Monitoring
Log Indicators:
- Unusual SSH login patterns for first-time users
- Unexpected root group assignments in auth logs
Network Indicators:
- SSH connections from unexpected sources followed by privilege escalation attempts
SIEM Query:
source="auth.log" AND "Accepted publickey" AND "first-time" AND "gid=0"