K3s’s etcd snapshot decompression can extract ZIP archive members with malicious names and write them to arbitrary filesystem locations. This allows an attacker who can trigger a restore operation to create or overwrite any file on the host, potentially compromising the Kubernetes cluster. The weakness is a classic directory traversal flaw (CWE-22).

The vulnerability affects K3s releases older than 1.35.3+k3s1, 1.34.6+k3s1, and v1.33.10+k3s1. Administrators using these versions and performing etcd snapshot restores are impacted.

The CVSS score of 5.8 reflects a moderate severity. No EPSS data is available, so the likelihood of exploitation is unknown. The flaw is not listed in the CISA KEV catalog. Based on the description, the attack vector requires the attacker to trigger a restore of a maliciously crafted ZIP file; thus the attacker must have administrative access to the K3s control plane or the ability to supply snapshot archives.