# CVE-2026-101304: FreeBSD jail fdescfs filesystem root escape via FD_RESOLVE_BENEATH bypass

Source: https://junglewise.ai/threats/cve-2026-101304-when-fdescfs-4-was-mounted-in-a-jail-with-the-nodup-option  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-15. Updated: 2026-10-20  
License: CC BY 4.0 with a link back

CVE-2026-101304 · Severity: high · CVSS 7.1 · Published 2026-10-15

FreeBSD jails isolate processes to prevent access outside a confined filesystem root, a key security feature for multi-tenant systems. A flaw in the fdescfs filesystem handler allows a jailed process to bypass these restrictions when the parent process passes a directory descriptor into the jail. An attacker can escape the jail's filesystem boundaries and access files outside the intended restricted area.

Technologies: [Freebsd](https://junglewise.ai/threats/technologies/freebsd). Vendors: [Freebsd](https://junglewise.ai/threats/vendors/freebsd).

## Quick answers

**Is CVE-2026-101304 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-101304 being exploited in the wild.

**How severe is CVE-2026-101304?** High severity, with a CVSS score of 7.1, published 15 October 2026.

**Which products and versions are affected?** Freebsd All supported versions; fixed in 15.1-RELEASE-p4, 15.0-RELEASE-p14, 14.5-RELEASE-p1, 14.4-RELEASE-p10, and stable branches.

**Is there a fix for CVE-2026-101304?** Yes: fixed in FreeBSD 15.1-RELEASE-p4, 15.0-RELEASE-p14, 14.5-RELEASE-p1, 14.4-RELEASE-p10, stable/15-n285682, stable/14-n275243. Until then: No workaround is available; however, systems that do not pass directory file descriptors into jails are not affected. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-101304 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-101304?** Check whether you run Freebsd at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in FreeBSD 15.1-RELEASE-p4, 15.0-RELEASE-p14, 14.5-RELEASE-p1, 14.4-RELEASE-p10, stable/15-n285682, stable/14-n275243

No workaround is available; however, systems that do not pass directory file descriptors into jails are not affected.

## Technical details

When fdescfs(4) is mounted in a jail with the "nodup" option, opening /dev/fd/N does not inherit the FD_RESOLVE_BENEATH flag or Capsicum capability rights from descriptor N. This allows a jailed process that has received a directory file descriptor from another jail to bypass the FD_RESOLVE_BENEATH restriction and escape the jail's filesystem root. The vulnerability affects all supported FreeBSD versions and requires the attacker to receive a directory file descriptor in the jail context.

## Affected products

- FreeBSD FreeBSD All supported versions; fixed in 15.1-RELEASE-p4, 15.0-RELEASE-p14, 14.5-RELEASE-p1, 14.4-RELEASE-p10, and stable branches

## Timeline

- 2026-09-29: disclosed
- 2026-09-29: patched
- 2026-10-15: advisory

## References

- [https://security.freebsd.org/advisories/FreeBSD-SA-26:66.jail.asc](https://security.freebsd.org/advisories/FreeBSD-SA-26:66.jail.asc)

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