CVE-2026-42575: apko doesn't verify downloaded apk packages against APKINDEX checksum (package substitution possible)

apko verifies the signature on APKINDEX.tar.gz but never compares individually downloaded .apk packages against the checksum recorded in the signed index. The checksum is parsed and available via ChecksumString(), and the downloaded package control hash is computed, but the two values are never compared in getPackageImpl(). Mismatched packages are silently accepted. An attacker who can substitute download responses (compromised mirror, HTTP repository, poisoned CDN cache) can install arbitrary packages into built images.

Fix: No fix available yet.

Acknowledgements

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