Bug 2539569 (CVE-2026-96808)

Summary: CVE-2026-96808 flatpak: Flatpak: Local privilege escalation via symlink traversal in revokefs writer
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
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Priority: high    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Flatpak. A malicious local user in an active local session could exploit a symlink traversal vulnerability in the `revokefs` writer. This flaw allows an attacker to modify files belonging to a different `revokefs` session after they have been validated. Consequently, an attacker could tamper with `ostree` commit objects, leading to root-controlled file writes and local root privilege escalation.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2539622    
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Description OSIDB Bzimport 2026-09-23 17:21:34 UTC 
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.