[!NOTE] Some vendors were given a pre-release version of this release. This public release includes two extra patches to fix regressions discovered very late during the embargo period and were thus not included in the pre-release versions. Please update to this version.

This release contains fixes for three high-severity security vulnerabilities in runc (CVE-2025-31133, CVE-2025-52565, and CVE-2025-52881). All three vulnerabilities ultimately allow (through different methods) for full container breakouts by bypassing runc's restrictions for writing to arbitrary /proc files.

Security

• CVE-2025-31133 exploits an issue with how masked paths are implemented in runc. When masking files, runc will bind-mount the container's /dev/null inode on top of the file. However, if an attacker can replace /dev/null with a symlink to some other procfs file, runc will instead bind-mount the symlink target read-write. This issue affected all known runc versions.

• CVE-2025-52565 is very similar in concept and application to CVE-2025-31133, except that it exploits a flaw in /dev/console bind-mounts. When creating the /dev/console bind-mount (to /dev/pts/$n), if an attacker replaces /dev/pts/$n with a symlink then runc will bind-mount the symlink target over /dev/console. This issue affected all versions of runc >= 1.0.0-rc3.

• CVE-2025-52881 is a more sophisticated variant of CVE-2019-19921, which was a flaw that allowed an attacker to trick runc into writing the LSM process labels for a container process into a dummy tmpfs file and thus not apply the correct LSM labels to the container process. The mitigation we applied for was fairly limited and effectively only caused runc to verify that when we write LSM labels that those labels are actual procfs files. This issue affects all known runc versions.

Added

• runc update now supports configuring per-device weights and iops. (#4775, #4807, #4825, #4931)

Static Linking Notices

The runc binary distributed with this release are statically linked with the following GNU LGPL-2.1 licensed libraries, with runc acting as a "work that uses the Library":

• libseccomp

The versions of these libraries were not modified from their upstream versions, but in order to comply with the LGPL-2.1 (§6(a)), we have attached the complete source code for those libraries which (when combined with the attached runc source code) may be used to exercise your rights under the LGPL-2.1.

However we strongly suggest that you make use of your distribution's packages or download them from the authoritative upstream sources, especially since these libraries are related to the security of your containers.

Thanks to the following contributors for making this release possible:

• Akihiro Suda akihiro.suda.cz@hco.ntt.co.jp
• Aleksa Sarai cyphar@cyphar.com
• Kir Kolyshkin kolyshkin@gmail.com
• Lei Wang ssst0n3@gmail.com
• Li Fubang lifubang@acmcoder.com
• Rodrigo Campos rodrigoca@microsoft.com
• Tõnis Tiigi tonistiigi@gmail.com

Signed-off-by: Aleksa Sarai cyphar@cyphar.com