This vulnerability in GNU tar arises from improper link resolution during archive extraction with the --one-top-level option. Hardlink targets are not confined to the specified top-level directory and may resolve relative to the extraction working directory. An attacker can craft an archive that creates hardlinks escaping the intended directory boundary. When combined with existing symbolic links under the working directory, this can lead to arbitrary file writes outside the extraction directory during a single extraction operation. The flaw is specific to the use of --one-top-level and does not affect default extraction behavior.

An attacker who can supply a crafted archive and cause it to be extracted with the --one-top-level option may be able to write files outside the intended extraction directory. This could lead to modification of unexpected files, potentially bypassing security mechanisms relying on file integrity. The confidentiality and integrity impacts are rated low, with no availability impact. The vulnerability requires local access and user interaction (extracting the archive).

Red Hat advises not to use the --one-top-level option as the sole confinement mechanism when extracting untrusted archives. Instead, extract archives as an unprivileged user into a freshly created empty directory after changing into that directory. Avoid extracting as root from sensitive directories such as /. Follow GNU tar security guidance for handling untrusted archives. Currently, no fixed packages are available; users should apply these mitigations until a fix is released. Patch status is not yet confirmed — check the Red Hat advisory at https://access.redhat.com/security/cve/CVE-2026-18508 for updates.