Executive brief
sm-crypto is a JavaScript library that implements SM2, a widely-used cryptographic signature algorithm. A flaw in its signature verification logic allows attackers to forge valid signatures for arbitrary keys, potentially enabling unauthorized document signing, authentication bypass, or transaction spoofing in applications relying on SM2 signatures for integrity protection.
Technical details
A signature forgery vulnerability exists in the SM2-DSA signature verification implementation due to improper cryptographic signature validation (CWE-347). Under default configurations, an attacker can craft valid signatures for arbitrary public keys without possessing the corresponding private key. The attack requires network access to the application consuming sm-crypto, with no authentication or user interaction needed. If the message format contains sufficient redundancy, an attacker can control the message prefix while maintaining signature validity, enabling targeted forgery attacks. The vulnerability affects all versions prior to 0.4.0, which contains the fix.
Affected products
- JuneAndGreen sm-crypto <0.4.0
Timeline
- 2026-01-21: disclosed: Vulnerability published on GitHub Security Advisory
- 2026-01-21: patched: Fixed in version 0.4.0