RUSTSEC-2026-0109: Broken hard revocation handling

What to do

1. See which version you have: cargo tree -i sequoia-git (it also shows which of your dependencies pulls it in).
2. Update within your version requirement: cargo update -p sequoia-git. If the fix is a newer major or minor than your requirement allows, raise it in Cargo.toml (for example sequoia-git = "0.6.0") or update the dependency that pulls it in.
3. Check again with cargo audit, or paste your Cargo.lock into our Cargo.toml checker.

Details from the advisory

Before sq-git checks if a commit can be authenticated, it first looks for hard revocations. Because parsing a policy is expensive and a project's policy rarely changes, sq-git has an optimization to only check a policy if it hasn't checked it before. It does this by maintaining a set of policies that it had already seen keyed on the policy's hash. Unfortunately, due to a bug the hash was truncated to be 0 bytes and thus only hard revocations in the target commit were considered. Normally this is not a problem as hard revocations are not removed from the signing policy.

An attacker could nevertheless exploit this flaw as follows. Consider Alice and Bob who maintain a project together. If Bob's certificate is compromised and Bob issues a hard revocation, Alice can add it to the project's signing policy. An attacker who has access to Bob's key can then create a merge request that strips the hard revocation. If Alice merges Bob's merge request, then the latest commit will not carry the hard revocation, and sq-git will not see the hard revocation when authenticating that commit or any following commits.

Note: for this attack to be successful, Alice needs to be tricked into merging the malicious MR. If Alice is reviewing MRs, then she is likely to notice changes to the signing policy.

Reported-by: Hassan Sheet

References

• Package: crates.io/crates/sequoia-git
• Advisory: rustsec.org/advisories/RUSTSEC-2026-0109.html
• Web: gitlab.com/sequoia-pgp/sequoia-git/-/commit/f9c9074bd80023456221f09c3c4ff19957ee9c58

From the RustSec Advisory Database (CC0-1.0) via the OSV export, downloaded Oct 24, 2026. Severity score computed from the published CVSS vector.