Unvollständige Privileg-Reduktion für com.system76.CosmicGreeter.GetUserData

The core impact of this TOCTOU race condition lies in the potential for privilege escalation. An attacker can exploit the race condition to regain privileges that the system intended to drop, effectively bypassing security controls. This could allow them to perform actions with elevated permissions, such as modifying system files, installing malicious software, or accessing sensitive data. The scope of the impact depends on the privileges that can be regained, but it represents a significant security risk. While specific attack scenarios are not detailed, the nature of TOCTOU vulnerabilities suggests that careful timing and manipulation of system state are required for successful exploitation.

Users of Pop!_OS and other Linux distributions that include cosmic-greeter are at risk, particularly those using older, unpatched versions. Systems with custom configurations or modifications to cosmic-greeter may be more vulnerable if the fix was not properly integrated. Shared hosting environments where multiple users share the same system resources are also at increased risk.

• linux / server: Monitor system logs (journalctl) for unusual privilege escalation attempts or errors related to cosmic-greeter. Specifically, look for processes unexpectedly gaining elevated privileges after a user login.

journalctl -u cosmic-greeter -f | grep -i privilege

• linux / server: Use auditd to track file access patterns related to cosmic-greeter and identify any suspicious modifications or access attempts.

auditctl -w /usr/bin/cosmic-greeter -p warx -k cosmic_greeter_audit

• linux / server: Employ tools like lsof or ps to monitor processes running under the cosmic-greeter user and identify any unexpected or unauthorized activity.

ps aux | grep cosmic-greeter
lsof -u cosmic-greeter

1. 2026-03-30Disclosure

   disclosure

1. Reserviert2026-02-05
2. Veröffentlicht2026-03-30
3. Geändert2026-04-16
4. EPSS aktualisiert2026-04-06

The primary mitigation for CVE-2026-25704 is to upgrade to the patched version of cosmic-greeter available in the GitHub pull request: https://github.com/pop-os/cosmic-greeter/pull/426. This update addresses the race condition by implementing more robust synchronization mechanisms. There are no immediate rollback steps, as the vulnerability is inherent in the pre-patched code. Consider implementing stricter access controls and monitoring system activity for suspicious behavior. After upgrading, verify the fix by attempting to trigger the race condition using known techniques and confirming that the privilege escalation is prevented.