FreeBSD nullfs Mount privileges management

Summaryinfo

A vulnerability was found in FreeBSD. It has been rated as critical. This vulnerability affects unknown code of the component nullfs Mount Handler. This manipulation causes privileges management. This vulnerability is registered as CVE-2025-15576. No exploit is available. It is suggested to install a patch to address this issue.

Detailsinfo

A vulnerability has been found in FreeBSD (version unknown) and classified as critical. Affected by this vulnerability is an unknown function of the component nullfs Mount Handler. The manipulation with an unknown input leads to a privileges management vulnerability. The CWE definition for the vulnerability is CWE-269. The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

If two sibling jails are restricted to separate filesystem trees, which is to say that neither of the two jail root directories is an ancestor of the other, jailed processes may nonetheless be able to access a shared directory via a nullfs mount, if the administrator has configured one. In this case, cooperating processes in the two jails may establish a connection using a unix domain socket and exchange directory descriptors with each other. When performing a filesystem name lookup, at each step of the lookup, the kernel checks whether the lookup would descend below the jail root of the current process. If the jail root directory is not encountered, the lookup continues. In a configuration where processes in two different jails are able to exchange file descriptors using a unix domain socket, it is possible for a jailed process to receive a directory for a descriptor that is below that process' jail root. This enables full filesystem access for a jailed process, breaking the chroot. Note that the system administrator is still responsible for ensuring that an unprivileged user on the jail host is not able to pass directory descriptors to a jailed process, even in a patched kernel.

The advisory is shared at security.freebsd.org. This vulnerability is known as CVE-2025-15576 since 02/09/2026. The exploitation appears to be easy. The exploitation requires an enhanced level of successful authentication. Neither technical details nor an exploit are publicly available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 03/17/2026). MITRE ATT&CK project uses the attack technique T1068 for this issue.

Applying a patch is able to eliminate this problem.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Type

• Operating System

Name

• FreeBSD

License

• open-source

Website

• Product: https://www.freebsd.org/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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