The FreeBSD Project has disclosed a critical security vulnerability, tracked as CVE-2025-15576, which allows attackers to escape jail environments and gain unauthorized access to the full host filesystem.
This flaw impacts FreeBSD versions 14.3 and 13.5, leaving unpatched systems exposed to severe security risks.
FreeBSD Vulnerabilities
FreeBSD jails are a powerful operating system-level virtualization technology. System administrators use them to safely isolate processes within a restricted, chroot-like environment.
Under normal conditions, a jailed process is strictly confined to its specific filesystem tree. This acts as a robust security boundary to prevent an isolated process from compromising the broader host system.
The vulnerability arises from an interaction involving nullfs mounts and Unix domain sockets.
The nullfs component is a pseudo-filesystem allowing administrators to mount directories elsewhere in the hierarchy. Unix domain sockets act as a local interprocess communication mechanism.
To exploit this issue, an attacker needs control over processes running in two separate, sibling jails.
These jails must share access to a common directory via a configured nullfs mount.
When these conditions are met, cooperating malicious processes can establish a connection using a Unix domain socket located in the shared directory. Through this socket, they pass directory file descriptors.
During a standard filesystem name lookup, the kernel checks whether the operation attempts to descend below the assigned jail root. However, during this specific exchange, the boundary validation is flawed.
If the kernel fails to encounter the jail root directory during the lookup, the restriction is bypassed.
A jailed process can receive a directory descriptor pointing outside its confined environment. This breaks the chroot isolation mechanism, granting full access to the host filesystem.
| Category | Detail |
|---|---|
| CVE ID | CVE-2025-15576 |
| Component | Core / Jail Module |
| Affected Versions | FreeBSD 14.3, FreeBSD 13.5 |
| Exploit Condition | Requires shared nullfs mount and unix domain socket |
| Workaround Available | None |
| Patch Available | Yes |
The impact of CVE-2025-15576 is severe because it defeats the primary purpose of FreeBSD jails.
Escaping the chroot environment allows malicious actors to access or execute files on the underlying host system, potentially leading to complete infrastructure compromise.
There are no known workarounds to mitigate this vulnerability. Administrators must upgrade their vulnerable systems immediately.
The FreeBSD Project has released security updates for all affected branches. Users can secure their infrastructure by running the standard fetch and install commands via the FreeBSD update utility, followed by a system reboot.
Alternatively, administrators managing custom builds can manually download the source code patches, verify the PGP signatures, recompile their kernel, and reboot to ensure the updates take effect.
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