Improper Validation of Specified Index, Position, or Offset in Input vulnerability in Google go-attestation. parseEfiSignatureList() does not advance the buffer past vendor bytes before reading entries. For hashSHA256SigGUID lists, this allows attacker-controlled vendor header bytes to be appended to the trusted SHA256 hash list. A crafted TPM event log could inject arbitrary SHA256 hashes into the verifier's trusted measurement database, enabling a remote attestation verifier to accept a compromised boot state. This issue affects go-attestation: through 0.6.0.

Affected: Go: github.com/google/go-attestation

## Summary

`parseEfiSignatureList()` in `attest/internal/events.go` does not skip `SignatureHeaderSize` vendor bytes before reading `EFI_SIGNATURE_LIST` signature entries, violating UEFI specification section 31.4.1.

## Impact

For `hashSHA256SigGUID` lists, attacker-controlled vendor header bytes are appended directly to the trusted SHA256 hash list. A crafted TPM event log can inject arbitrary SHA256 hashes into the verifier's trusted measurement database, allowing a remote attestation verifier to accept a compromised boot state as legitimate — breaking the core integrity guarantee of remote attestation.

## Root Cause

After `binary.Read(&signatures.Header)` reads 28 bytes, `buf` points to the start of the `SignatureHeaderSize` vendor bytes. Both entry loops start at `sigOffset := 0` instead of `sigOffset := SignatureHeaderSize`, causing vendor bytes to be read as signature entries.

## Affected versions

All versions through commit `f877374` (2026-05-15).

## Fix

Pull request: https://github.com/google/go-attestation/pull/502

- Add bound check: `SignatureHeaderSize` must not exceed remaining list space - Skip `SignatureHeaderSize` bytes before both entry loops - Regression test: `TestParseEfiSignatureListNonZeroSignatureHeaderSize`

Affected: Ubuntu:26.04:LTS: golang-github-google-go-attestation

Improper Validation of Specified Index, Position, or Offset in Input vulnerability in Google go-attestation. parseEfiSignatureList() does not advance the buffer past vendor bytes before reading entries. For hashSHA256SigGUID lists, this allows attacker-controlled vendor header bytes to be appended to the trusted SHA256 hash list. A crafted TPM event log could inject arbitrary SHA256 hashes into the verifier's trusted measurement database, enabling a remote attestation verifier to accept a compromised boot state. This issue affects go-attestation: through 0.6.0.