CVE-2025-52881: runc: LSM labels can be bypassed with malicious config using dummy procfs files

Vulnerability summary

CVE-2025-52881 is a high (CVSS 7.5) UNIX Symbolic Link (Symlink) Following vulnerability in linuxfoundation runc. EPSS estimates a 0.80% chance of exploitation in the next 30 days, higher than 56.7% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 06-11-2025
   PublishedVulnerability first disclosed.
2. 06-11-2025
   Last modifiedVulnerability information updated.

Description

runc is a CLI tool for spawning and running containers according to the OCI specification. In versions 1.2.7, 1.3.2 and 1.4.0-rc.2, an attacker can trick runc into misdirecting writes to /proc to other procfs files through the use of a racing container with shared mounts (we have also verified this attack is possible to exploit using a standard Dockerfile with docker buildx build as that also permits triggering parallel execution of containers with custom shared mounts configured). This redirect could be through symbolic links in a tmpfs or theoretically other methods such as regular bind-mounts. While similar, the mitigation applied for the related CVE, CVE-2019-19921, was fairly limited and effectively only caused runc to verify that when LSM labels are written they are actually procfs files. This issue is fixed in versions 1.2.8, 1.3.3, and 1.4.0-rc.3.

• CWE-61UNIX Symbolic Link (Symlink) FollowingThe product, when opening a file or directory, does not sufficiently account for when the file is a symbolic link that resolves to a target outside of the intended control sphere. This could allow an attacker to cause the product to operate on unauthorized files.
• CWE-363Race Condition Enabling Link FollowingThe product checks the status of a file or directory before accessing it, which produces a race condition in which the file can be replaced with a link before the access is performed, causing the product to access the wrong file.