cggmp24 and cggmp21 are vulnerable to signature forgery through altered presignatures

Impact

This attack is against presignatures used in very specific context:

• Presignatures + HD wallets derivation: security level reduces to 85 bits
  Previously users could generate a presignature, and then choose a HD derivation path while issuing a partial signature via Presignature::set_derivation_path, which is malleable to attack that reduces target security level. To mitigate, this method has been removed from API.
• Presignatures + "raw signing" (when signer signs a hash without knowing an original message): results into signature forgery attack
  Previously, users were able to configure Presignature::issue_partial_signature with hashed message without ever providing original mesage. In new API, this method only accepts digests for which original message has been observed.

Patches

cggmp24 v0.7.0-alpha.2 release contains API changes that make it impossible to use presignatures in contexts in which it reduces security. Follow migration guidelines to upgrade.

Workarounds

Users can continue using un-patched versions of library as long as they don't use presignatures in said scenarios where it weakens system security. To be sure, migrate to patched version that excludes presignatures from being used in such scenarios.

References

Read this blog post to learn more.