Advisories for Golang/Github.com/Sigstore/Gitsign package

gitsign verify and gitsign verify-tag re-encode commit/tag objects through go-git's EncodeWithoutSignature before checking the signature, instead of verifying against the raw git object bytes. For malformed objects with duplicate tree headers, git-core and go-git parse different trees: git-core uses the first, go-git uses the second. A signature crafted over the go-git-normalized form (second tree) passes gitsign verify while git-core resolves the commit to a completely different tree. This breaks the …

CertVerifier.Verify() in pkg/git/verifier.go unconditionally dereferences certs[0] after sd.GetCertificates() without checking the slice length. A CMS/PKCS7 signed message with an empty certificate set is a structurally valid DER payload; GetCertificates() returns an empty slice with no error, causing an immediate index-out-of-range panic. On the gitsign –verify code path (the GPG-compatible mode invoked by git verify-commit), the panic is silently recovered by internal/io/streams.go's Wrap() function, which returns nil instead of an error. …

gitsign may select the wrong Rekor entry to use during online verification when multiple entries are returned by the log.

This advisory duplicates another.

Gitsign is software for keyless Git signing using Sigstore. In versions of gitsign starting with 0.6.0 and prior to 0.8.0, Rekor public keys were fetched via the Rekor API, instead of through the local TUF client. If the upstream Rekor server happened to be compromised, gitsign clients could potentially be tricked into trusting incorrect signatures. There is no known compromise the default public good instance (rekor.sigstore.dev) - anyone using this …