FreeBSD: Jail filesystem root escape via file descriptor passing
Summary
FreeBSD jails confine processes to a restricted view of the filesystem. Due to a flaw in SCM_RIGHTS descriptor passing, a process in a jail that has received a directory file descriptor from another jail can clear the FD_RESOLVE_BENEATH restriction by sending the descriptor to itself over a Unix domain socket, and then escape the jail's filesystem root. The attacker needs a local process inside the jail; the advisory describes no remote attack path. This CVE is one of three jail escape flaws fixed together in FreeBSD-SA-26:66.
Affected
- FreeBSD 15.1-RELEASE to before 15.1-RELEASE-p4
- FreeBSD 15.0-RELEASE to before 15.0-RELEASE-p14
- FreeBSD 14.5-RELEASE to before 14.5-RELEASE-p1
- FreeBSD 14.4-RELEASE to before 14.4-RELEASE-p10
- Default configuration: unknown
Fixed in
- FreeBSD 15.1-RELEASE-p4 or later
- FreeBSD 15.0-RELEASE-p14 or later
- FreeBSD 14.5-RELEASE-p1 or later
- FreeBSD 14.4-RELEASE-p10 or later
- Stable and releng branches dated after the correction date (29 September 2026), followed by a reboot
Workaround
No workaround is available. Systems that do not pass directory file descriptors into jails are not affected.
Exploitation
- CISA SSVC: exploitation none, automatable yes, technical impact total
- Not listed in CISA KEV
- Tenable: no known exploits
- No public proof of concept confirmed; unverified
Our recommendation
- Update FreeBSD hosts with jails to a fixed patch level listed above and reboot.
- Systems on FreeBSD 15.0 need an upgrade to a supported release, because 15.0 reaches end of life on 30 September 2026 (secondary source).
- Check whether any jail receives directory file descriptors from other jails, for example through shared nullfs mounts or Unix sockets, and restrict this where it is not needed.
- Note that severity scores differ between sources; base prioritisation on the vendor advisory.
- Monitor jail hosts for unexpected filesystem access outside jail roots.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- FreeBSD-SA-26:66.jail Security Advisory security.freebsd.org
- VulDB CVE-2026-101306 (severity discrepancies) vuldb.com
- Tenable plugin 353461 (exploit status) www.tenable.com
- Strix CVE-2026-101306 (secondary reference) www.strix.ai
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 30 Oct 2026, 17:52.
Original description (NVD)
SCM_RIGHTS file descriptor passing did not preserve FD_RESOLVE_BENEATH when a descriptor was transferred. A process could clear the restriction by sending the descriptor to itself over a Unix domain socket. A process in a jail that has received a directory file descriptor from another jail can use these techniques to escape the jail's filesystem root restriction.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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