Incomplete privilege drop for com.system76.CosmicGreeter.GetUserData

[nixpkgs-security-tracker]

• CVE-2026-25704
• Nixpkgs security tracker issue
• affected package maintainers: cc @ahoneybun, @a-kenji, @thefossguy, @HeitorAugustoLN, @michaelBelsanti, @alyssais, @drakon64, @nyabinary, @Pandapip1

Description

A Privilege Dropping / Lowering Errors/Time-of-check Time-of-use (TOCTOU) Race Condition vulnerability in  cosmic-greeter can allow an attacker to regain privileges that should have been dropped and abuse them in the racy checking logic.

This issue affects cosmic-greeter before https://github.Com/pop-os/cosmic-greeter/pull/426.

Affected packages

• cosmic-greeter (1.0.0@nixos-25.11, 1.0.8@nixos-unstable)

Additional comment

https://bugzilla.suse.com/show_bug.cgi?id=CVE-2026-25704

[a-kenji]

As far as I know we addressed this on 13.03.26 in: 64db9dd for unstable.
It has not been backported to the stable release as of yet.

Edit:

• backport here: [25.11] cosmic-greeter: apply upstream patch for security hardening #505350

[a-kenji]

Backport has landed in all supported channels: https://nixpk.gs/pr-tracker.html?pr=505350