Bug 2539421 (CVE-2026-96281) - CVE-2026-96281 flatpak: flatpak: Unprivileged active user can bypass anti-downgrade checks for system apps/runtimes
Summary: CVE-2026-96281 flatpak: flatpak: Unprivileged active user can bypass anti-dow...
Keywords:
Status: NEW
Alias: CVE-2026-96281
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
medium
medium
Target Milestone: ---
Assignee: Product Security
QA Contact:
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2026-09-23 14:03 UTC by OSIDB Bzimport
Modified: 2026-09-27 20:56 UTC (History)
2 users (show)

Fixed In Version:
Clone Of:
Environment:
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Attachments (Terms of Use)

Description OSIDB Bzimport 2026-09-23 14:03:18 UTC 
GHSA-q4gr-vc25-57m5 (https://github.com/flatpak/flatpak/security/advisories/GHSA-q4gr-vc25-57m5)

Description: By using the system helper's unprivileged RemoveLocalRef method, an attacker was able to remove the remote ref of the app or runtime. The anti-downgrade check would fail to find the remote ref, and with it the date to check against, allowing an attacker to bypass the check and downgrade apps.

Mitigation: Ensure that Flatpak apps installed system-wide are fully updated before running them. Fixed in 1.18.1 (backports available for 1.16.x). Discovered and reported by BreachX Zero Day Labs, using Typhon AI Mil v2. Contributing Researcher: Vivek Parikh.
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