CVE-2026-96808: High severity Flatpak Flatpak vulnerability
In Flatpak before 1.18.1, the revokefs writer, used by the flatpak-system-helper to receive repository data from unprivileged callers, validated file paths by rejecting literal .. components but did not prevent symlink traversal. A malicious local user in an active local session could obtain two revokefs sessions via the system helper, create a symlink in one session pointing into the other session's directory, and retain a file descriptor through that symlink. This allowed the attacker to modify files belonging to a different revokefs session after they had been validated and imported by the system helper. In particular, an attacker could use this to tamper with ostree commit objects in the system repository after they passed signature verification, enabling root-controlled file writes to attacker-chosen paths and local root privilege escalation.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Flatpakto a version that resolves this vulnerability.Fixed in 1.18.1
Event History
Frequently Asked Questions
Who is exposed to exploitation?
A malicious local user must have an active local session and be able to interact with the system helper. The issue can lead to local root privilege escalation.
What does an attacker need to do to exploit this?
The attacker needs to obtain two revokefs sessions through the system helper, create a symlink from one session into the other session's directory, and retain a file descriptor through that symlink. This bypasses the writer's validation of literal '..' path components.
What is the impact after successful exploitation?
An attacker can modify files in another revokefs session after validation and import. This can include tampering with OSTree commit objects after signature verification, resulting in root-controlled writes to attacker-chosen paths.
Which versions are affected?
Flatpak versions before 1.18.1 are affected.