CVE-2023-25809: rootless: `/sys/fs/cgroup` is writable when cgroupns isn't unshared in runc

Vulnerability summary

CVE-2023-25809 is a medium (CVSS 6.3) Improper Preservation of Permissions vulnerability in linuxfoundation runc. EPSS estimates a 0.32% chance of exploitation in the next 30 days, higher than 24.9% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 29-03-2023
   PublishedVulnerability first disclosed.
2. 12-02-2025
   Last modifiedVulnerability information updated.

Description

runc is a CLI tool for spawning and running containers according to the OCI specification. In affected versions it was found that rootless runc makes `/sys/fs/cgroup` writable in following conditons: 1. when runc is executed inside the user namespace, and the `config.json` does not specify the cgroup namespace to be unshared (e.g.., `(docker|podman|nerdctl) run --cgroupns=host`, with Rootless Docker/Podman/nerdctl) or 2. when runc is executed outside the user namespace, and `/sys` is mounted with `rbind, ro` (e.g., `runc spec --rootless`; this condition is very rare). A container may gain the write access to user-owned cgroup hierarchy `/sys/fs/cgroup/user.slice/...` on the host . Other users's cgroup hierarchies are not affected. Users are advised to upgrade to version 1.1.5. Users unable to upgrade may unshare the cgroup namespace (`(docker|podman|nerdctl) run --cgroupns=private)`. This is the default behavior of Docker/Podman/nerdctl on cgroup v2 hosts. or add `/sys/fs/cgroup` to `maskedPaths`.

• CWE-281Improper Preservation of PermissionsThe product does not preserve permissions or incorrectly preserves permissions when copying, restoring, or sharing objects, which can cause them to have less restrictive permissions than intended.