The vulnerability is a classic zip slip flaw in the Unarchive function of fission’s pkg/utils/zip.go. The function concatenates each archive entry name to the destination directory without validating that the resolved path remains within that directory. Consequently, an attacker who can supply the archive URL used by the fission‑fetcher sidecar could craft entries such as ../../tmp/evil, causing files to be written as /tmp/evil. This results in remote write access that may overwrite configuration files, secret volumes, or files in other tenants’ packaging directories on the host node, potentially leading to privilege escalation or severe data corruption.

The flaw exists in all versions of the fission framework released before 1.25.0. The issue operates when the fetcher sidecar, running as a per‑environment pod, downloads a Package.Spec.Source.URL or Deployment.URL archive that the attacker can control. Users running any vulnerable fission installation, regardless of cluster configuration, are affected.

The CVSS score of 7.7 indicates a high severity level. The EPSS score is not available, suggesting that currently known exploit activity is not high, but the flaw remains serious due to its impact. The flaw is not listed in the CISA KEV catalog. Exploitation would typically require an attacker to supply a malicious zip archive to a fetcher pod, which has local host and write privileges. In a multi‑tenant Kubernetes environment, this could allow lateral movement and compromise of other namespaces, including secret and config map volumes. If the fetcher sidecar is running with elevated privileges, the attacker could also overwrite files necessary for the fission runtime or other pods. The attack vector is local but relies on the fetcher’s ability to fetch arbitrary URLs, making it a potentially critical vector in exposed environments.