Summary

A path traversal vulnerability exists in K3s's etcd snapshot decompression functionality. Zip files containing archive members with maliciously crafted names (e.g., ../../../../etc/password) can be written to arbitrary locations on the filesystem when an administrator restores the archive as a compressed etcd snapshot.

Mitigations

Enable golang's built-in insecure path protections when restoring snapshots by setting theGODEBUG environment variable: bash GODEBUG=zipinsecurepath=0 k3s server --cluster-reset --cluster-reset-restore-path=/path/to/snapshot.zip Manually extract the snapshot from the zip archive before restoring it. If the snapshot to be restored does not end with .zip, the vulnerable extraction code will not be executed.

Additional Notes

Administrators should be aware of the cautions noted in the "Security" section of the documentation on Restoring Snapshots.

CNCF K3s 1.32 before 1.32.4-rc1+k3s1 has a Kubernetes kubelet configuration change with the unintended consequence that, in some situations, ReadOnlyPort is set to 10255. For example, the default behavior of a K3s online installation might allow unauthenticated access to this port, exposing credentials.