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2026-03-29 — Forge signature forgery in RSA-PKCS due to ASN.1 extra field (GHSA-ppp5-5v6c-4jwp)

Product: Forge

Impact (per advisory): A malformed ASN.1 structure in RSA-PKCS signature handling could enable signature forgery.

Why this matters

Signature verification is a trust boundary. If the parser accepts extra or unexpected ASN.1 fields, an attacker may be able to produce a blob that verifies even though it should fail.

  • Patch/upgrade Forge to the fixed release.
  • Treat ASN.1 parsing as hostile input:
  • reject non-canonical encodings
  • fail on extra unexpected fields
  • verify against strict DER expectations where applicable
  • Add regression tests for malformed RSA-PKCS signature encodings.
  • Audit other cryptographic verification paths for lax parser behavior.

Detection / hunting ideas

  • Add tests that replay malformed ASN.1 signatures and confirm verification fails.
  • Review logs for signature-validation anomalies or unexpected accepted inputs.

References