Medium [CVE-2026-18477] TOCTOU in incremental dumpdir 'X' rename handling allows restore path escape

A TOCTOU (Time-of-Check Time-of-Use) vulnerability in GNU tar's incremental dumpdir 'X' rename handling allows a local attacker with write access to a directory being backed up to influence the restore process if the attacker has access to the system where the restore is being performed.

During restoration, files or directories may be created, renamed or overwritten outside the intended extraction directory. This could lead to unauthorized file modification or, in some cases, privilege escalation.

Exploitation does not require the attacker to modify or craft the archive, and standard backup and restore workflows—including extracting into a newly created directory without using the -P option do not mitigate the issue. This issue affects GNU tar incremental backup and restore (-g/-G).

A local attacker who can write to content included in an incremental backup, and who can also access the system where that backup is later restored, may cause the restore to create, rename, or overwrite paths outside the intended extraction directory via a TOCTOU race in dumpdir 'X' handling.

Red Hat is assessing impact for the tar package in supported products. Red Hat severity: Moderate — CVSS 4.4 (CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:N/I:H/A:N).

Weakness: CWE-367.