Vulnerability in GNU Tar

CVE-2026-18477

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.

Vulnerability class: TOCTOU (Time-of-Check to Time-of-Use)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 4.4 (Medium). Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:N/I:H/A:N.

EPSS exploit prediction

EPSS: 0.001 (0.1th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 0th percentile — 0.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-18477: held from 0.001 to 0.001.

EPSS over last 30 days · oldest: 0.001 · newest: 0.001 · change: 0.000

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-18477?
CVE-2026-18477 is a medium-severity vulnerability in GNU Tar, classified under Time-of-check Time-of-use (TOCTOU) Race Condition. CVSS score: 4.4/10. Published 2026-08-03.
How severe is CVE-2026-18477?
Medium severity. CVSS v3 base score is 4.4 out of 10.