CVE-2026-18477 Tar: tar: toctou in incremental dumpdir 'x' rename handling allows restore path escape

Description

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.

Exploitable with local access to the machine, with an ordinary account and if a user takes an action; an attacker can seriously compromise confidentiality, integrity or availability.

Attack vector

Local

Attack complexity

High

Privileges required

Low

Interaction

Required

Scope

Unchanged

Confidentiality

None

Integrity

High

Availability

None

Affected products and versions