Affected: Go: github.com/sigstore/rekor

## Summary

Rekor’s cose v0.0.1 entry implementation can panic on attacker-controlled input when canonicalizing a proposed entry with an empty `spec.message`. `validate()` returns nil (success) when `message` is empty, leaving `sign1Msg` uninitialized, and `Canonicalize()` later dereferences `v.sign1Msg.Payload`.

## Impact

A malformed proposed entry of the `cose/v0.0.1` type can cause a panic on a thread within the Rekor process. The thread is recovered so the client receives a 500 error message and service still continues, so the availability impact of this is minimal.

## Patches

Upgrade to v1.5.0

## Workarounds

None