Gitsign is a keyless Sigstore to signing tool for Git commits with your a GitHub / OIDC identity. From 0.4.0 to before 0.15.0, 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. main.go then exits with code 0, causing exit-code-only verification callers to interpret the failed verification as success. This vulnerability is fixed in 0.15.0.

Affected: Go: github.com/sigstore/gitsign

## Summary

`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. `main.go` then exits with code 0, causing exit-code-only verification callers to interpret the failed verification as success.

## Severity

**Medium** (CVSS 3.1: 5.8)

`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:L`

- **Attack Vector:** Network — attacker pushes a commit carrying a crafted signature to any accessible repository, or delivers the signature file out-of-band - **Attack Complexity:** Low — stripping certificates from a PKCS7 object requires only standard ASN.1 tooling - **Privileges Required:** None — writing to an accessible repo (or creating a repo a victim clones) is sufficient - **User Interaction:** Required — victim must run `git verify-commit`, `gitsign --verify`, or an equivalent verification step - **Scope:** Unchanged - **Confidentiality Impact:** None - **Integrity Impact:** Low — exit-code-only callers (scripts, some CI pipelines) treat the panicked verification as success; git's o…

Affected: Ubuntu:25.10: gitsign, Ubuntu:Pro:26.04:LTS: gitsign

Gitsign is a keyless Sigstore to signing tool for Git commits with your a GitHub / OIDC identity. From 0.4.0 to before 0.15.0, 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. main.go then exits with code 0, causing exit-code-only verification callers to interpret the failed verification as success. This vulnerability is fixed in 0.15.0.