Impact A bug was found in containerd where containers launched with a numeric "User" directive that cannot be parsed as a 32-bit integer are incorrectly treated as a username. If a crafted image provides an "/etc/passwd" file mapping this large numeric string to root, the container ultimately runs as root (UID 0). This allows the Kubernetes "runAsNonRoot" restriction to be bypassed, causing unexpected behavior for environments that require containers to run as a non-root user. Patches This bug has been fixed in the following containerd versions: * 2.3.1 * 2.2.4 * 2.0.9 * 1.7.32 Note: The containerd 2.1 release has reached its "end of life" (https://containerd.io/releases/#current-state-of-containerd-releases) and a fixed version is not provided. Users should update to these versions to resolve the issue. Workarounds Ensure that only trusted images are used and that only trusted users have permissions to import images. Alternatively, enforcing a specific numeric "runAsUser" in the Kubernetes Pod "securityContext" overrides the "USER" directive in the image and prevents the bypass. Newer versions of Kubernetes, starting with 1.34, also appear to enforce "runAsNonRoot" properly regardless of this bug. Credits The containerd project would like to thank Lei Wang (@ssst0n3) for responsibly disclosing this issue in accordance with the "containerd security policy" (https://github.com/containerd/project/blob/main/SECURITY.md). Resources * https://github.com/advisories/GHSA-265r-hfxg-fhmg (CVE-2024-40635) For more information If there are any questions or comments about this advisory: * Open an issue in "containerd" (https://github.com/containerd/containerd/issues/new/choose) * Send an email to "security@containerd.io" (mailto:security@containerd.io) To report a security issue in containerd: * "Report a new vulnerability" (https://github.com/containerd/containerd/security/advisories/new) * Send an email to "security@containerd.io" (mailto:security@containerd.io)