Medium [CVE-2026-18508] --one-top-level hardlink targets not confined to top-level directory enabling arbitrary file overwrite
This medium-severity Red Hat Linux advisory covers CVE-2026-18508 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat Discovery 2.
Aggregated and source-linked by VulniPulse. Data sources, validation and limitations.
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Summary
A flaw was found in GNU tar. When extracting an archive with the --one-top-level option, hardlink targets are not confined to the designated top-level directory and may resolve relative to the extraction working directory.
A crafted archive can create hardlinks that escape the intended boundary and, when combined with a preexisting symbolic link under the working directory, may allow writing outside that boundary during a single extraction. Red Hat Enterprise Linux is affected.
This issue only applies when the --one-top-level option is used to extract an untrusted archive. Default tar extraction without --one-top-level is not impacted by this specific boundary failure.
Users should avoid using --one-top-level as the sole confinement mechanism for untrusted archives until fixed packages are available. Red Hat severity: Moderate — CVSS 4.4 (CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N).
Weakness: CWE-59. Red Hat lists Red Hat Hardened Images as not affected.
Red Hat fixing advisory: RHSA-2026:61586, RHSA-2026:61581, RHSA-2026:61783, RHSA-2026:50807.
Affected products named by the advisory: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 9; Red Hat Discovery 2; Red Hat Enterprise Linux 6; and 4 more.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 26 days ago·verify at source
- tar-2:1.35-13.el10_2
- tar-2:1.34-13.el9_8
- discovery/discovery-server-rhel9:1788205779
- tar-main-1.35-9.2.hum1
- RHSA-2026:61586
- RHSA-2026:61581
- RHSA-2026:61783
- RHSA-2026:50807
Official advisory · high-confidence parse· fetched 26 days ago·verify at source
Mitigation checklist
- Do not use --one-top-level as the sole confinement mechanism when extracting untrusted archives. Prefer extracting as an unprivileged user into a freshly created empty directory after changing into that directory (mkdir and cd), avoid extracting as root from sensitive working directories such as /, and follow the GNU tar security guidance for untrusted archives.
Official advisory · high-confidence parse· fetched 26 days ago·verify at source
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