CVE-2026-28406: kaniko has tar archive path traversal in its build context extraction, allowing file writes outside destination directories

kaniko unpacks build context archives using filepath.Join(dest, cleanedName) without enforcing that the final path stays within dest. A tar entry like ../outside.txt escapes the extraction root and writes files outside the destination directory. In environments with registry authentication, this can be chained with docker credential helpers to achieve code execution within the executor process. Affected versions >= 1.25.4, <= 1.25.9.

Fix: Merged with PR #326 — uses securejoin for path resolution in tar extraction.

Acknowledgements

kaniko thanks Oleh Konko from 1seal for discovering and reporting this issue.