CVE-2026-46680: containerd user ID handling bypass allows runAsNonRoot evasion ### Impact A bug was found in containerd where containers launched with a numeric `User`…

high7.8

containerd user ID handling bypass allows runAsNonRoot evasion

### 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 [[email protected]](mailto:[email protected])

To report a security issue in containerd:
* [Report a new vulnerability](https://github.com/containerd/containerd/security/advisories/

Affected

4 ranges

Vendor	Product	Version range	Fixed in
github.com	containerd_containerd	>= 1.7.27 < 1.7.32	1.7.32
github.com	containerd_containerd_v2	>= 2.0.4 < 2.0.9	2.0.9
github.com	containerd_containerd_v2	>= 2.1.0-beta.0 < 2.2.4	2.2.4
github.com	containerd_containerd_v2	>= 2.3.0-beta.0 < 2.3.1	2.3.1

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