The vulnerability resides in the SM2 decryption routine of the sm-crypto library. By repeatedly calling the SM2 decryption interface, an attacker can recover the full private key after only a few hundred interactions. The success of this attack directly leaks the cryptographic secret, undermining all confidentiality and integrity guarantees that rely on SM2 keys.

The affected product is sm-crypto from JuneAndGreen. Any deployment running a version earlier than 0.3.14 is vulnerable. Version 0.3.14 and later contain the patch that fixes the recovery flaw.

The CVSS score of 9.1 classifies this flaw as critical. Although the EPSS score is below 1%, indicating a low current exploitation probability, the vulnerability is not listed in the CISA KEV catalog. An attacker must be able to invoke the SM2 decryption function, which is typically exposed through application code; therefore the attack vector is inferred to be through the application’s usage of the library rather than a network exploit. Given the high impact of private key leakage, the overall risk to any system that depends on SM2 remains significant until the library is updated.