TOCTOU in GNU tar incremental dumpdir rename
CVE-2026-18477 Published on August 3, 2026
Tar: tar: 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 workflowsincluding extracting into a newly created directory without using the -P option do not mitigate the issue.
Vulnerability Analysis
CVE-2026-18477 can be exploited with local system access, requires user interaction and a small amount of user privileges. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality, a high impact on integrity, and no impact on availability.
Timeline
Reported to Red Hat.
Made public.
Weakness Type
What is a TOCTTOU Vulnerability?
The software checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check. This can cause the software to perform invalid actions when the resource is in an unexpected state. This weakness can be security-relevant when an attacker can influence the state of the resource between check and use. This can happen with shared resources such as files, memory, or even variables in multithreaded programs.
CVE-2026-18477 has been classified to as a TOCTTOU vulnerability or weakness.
Products Associated with CVE-2026-18477
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