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7.5
Jailed processes can access shared directory via nullfs mount
CVE-2025-15576
Summary
A configuration issue allows jailed processes to break out of their restricted filesystems and access the entire system's files. This can happen if administrators use nullfs mounts to share directories between jailed processes. To prevent this, ensure that you're not sharing directories between jailed processes and use the patched kernel to prevent directory descriptor exchange.
Original title
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...
Original description
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.
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.
Vulnerability type
CWE-269
Improper Privilege Management
CWE-488
CWE-790
Published: 9 Mar 2026 · Updated: 13 Mar 2026 · First seen: 9 Mar 2026