cosign is a container signing and verification utility. In versions prior to 1.10.1 cosign can report a false positive if any attestation exists. cosign verify-attestation used with the --type flag will report a false positive verification when there is at least one attestation with a valid signature and there are NO attestations of the type being verified (--type defaults to "custom"). This can happen when signing with a standard keypair and with "keyless" signing with Fulcio.

This vulnerability can be reproduced with the distroless.dev/static@sha256:dd7614b5a12bc4d617b223c588b4e0c833402b8f4991fb5702ea83afad1986e2 image. This image has a vuln attestation but not an spdx attestation. However, if you run cosign verify-attestation --type=spdx on this image, it incorrectly succeeds.

This issue has been addressed in version 1.10.1 of cosign. Users are advised to upgrade. There are no known workarounds for this issue.