CRI-O vulnerable to /etc/passwd tampering resulting in Privilege Escalation

Impact

It is possible to craft an environment variable with newlines to add entries to a container's /etc/passwd. It is possible to circumvent admission validation of username/UID by adding such an entry.

Note: because the pod author is in control of the container's /etc/passwd, this is not considered a new risk factor. However, this advisory is being opened for transparency and as a way of tracking fixes.

Patches

1.26.0 will have the fix. More patches will be posted as they're available.

Workarounds

Additional security controls like SELinux should prevent any damage a container is able to do with root on the host. Using SELinux is recommended because this class of attack is already possible by manually editing the container's /etc/passwd

References