Description
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.
Published: 2026-09-23
Score: 7.4 High
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

Vendor Solution

Fixed in 1.18.1 by commits: * a3583bc https://github.com/flatpak/flatpak/commit/a3583bc87d4f86c2794ff879ea56fce95b0b0b5f "revokefs: Avoid symlink path traversal out of basefd in simple cases" * b00c7b5 https://github.com/flatpak/flatpak/commit/b00c7b5073a25bdc34653642de543b5ef6fe0225 "revokefs: Avoid symlink path traversal in link(), rename()" * 4ddb5dc https://github.com/flatpak/flatpak/commit/4ddb5dc0de1bd25e52627f520a49063d94f79377 "revokefs: Avoid symlink path traversal in symlink()" * e7f96b4 https://github.com/flatpak/flatpak/commit/e7f96b4d1533f735ace2ea21dbf770e8d4be465a "revokefs: Avoid symlink path traversal in chmod()" For LTS operating system distributions, backports of these changes are available in the flatpak-1.16.x branch.

Tracking

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Advisories

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History

Thu, 24 Sep 2026 00:15:00 +0000

Type Values Removed Values Added
Title Symlink Traversal in Flatpak Revokefs Enables Local Root Privilege Escalation flatpak: Flatpak: Local privilege escalation via symlink traversal in revokefs writer
Weaknesses CWE-59
References
Metrics threat_severity

None

threat_severity

Important


Wed, 23 Sep 2026 20:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Wed, 23 Sep 2026 19:00:00 +0000

Type Values Removed Values Added
Title Symlink Traversal in Flatpak Revokefs Enables Local Root Privilege Escalation

Wed, 23 Sep 2026 17:15:00 +0000

Type Values Removed Values Added
Description 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.
First Time appeared Flatpak
Flatpak flatpak
Weaknesses CWE-61
CPEs cpe:2.3:a:flatpak:flatpak:*:*:*:*:*:*:*:*
Vendors & Products Flatpak
Flatpak flatpak
References
Metrics cvssV3_1

{'score': 7.4, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H'}


cve-icon MITRE

Status: PUBLISHED

Assigner: mitre

Published:

Updated: 2026-09-23T18:22:46.208Z

Reserved: 2026-09-23T16:58:36.801Z

Link: CVE-2026-96808

cve-icon Vulnrichment

Updated: 2026-09-23T18:22:41.941Z

cve-icon NVD

Status : Received

Published: 2026-09-23T17:17:25.860

Modified: 2026-09-23T19:19:55.187

Link: CVE-2026-96808

cve-icon Redhat

Severity : Important

Publid Date: 2026-09-23T16:58:37Z

Links: CVE-2026-96808 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-09-24T02:30:13Z

Weaknesses
  • CWE-59

    Improper Link Resolution Before File Access ('Link Following')

  • CWE-61

    UNIX Symbolic Link (Symlink) Following