Flatpak up to 1.18.0 Revokefs Writer link following

Summaryinfo

A vulnerability described as very critical has been identified in Flatpak up to 1.18.0. The impacted element is an unknown function of the component Revokefs Writer. Such manipulation leads to link following. This vulnerability is traded as CVE-2026-96808. An attack has to be approached locally. There is no exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in Flatpak up to 1.18.0 and classified as very critical. Affected by this issue is an unknown code block of the component Revokefs Writer. The manipulation with an unknown input leads to a link following vulnerability. Using CWE to declare the problem leads to CWE-59. The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource. Impacted is confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-96808 since 09/23/2026. The exploitation is known to be easy. The attack needs to be approached locally. There are neither technical details nor an exploit publicly available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 09/23/2026).

Upgrading to version 1.18.1 eliminates this vulnerability.

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Productinfo

Name

• Flatpak

Version

• 1.0
• 1.1
• 1.2
• 1.3
• 1.4
• 1.5
• 1.6
• 1.7
• 1.8
• 1.9
• 1.10
• 1.11
• 1.12
• 1.13
• 1.14
• 1.15
• 1.16
• 1.17
• 1.18.0

Website

• Product: https://github.com/flatpak/flatpak/

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