|Type||Private key recovery|
The signing function in crypto/ecdsa/ecdsa_ossl.c in certain OpenSSL versions and forks is vulnerable to timing attacks when signing with the standardized elliptic curve P-256 despite featuring constant-time curve operations and modular inversion. A software defect omits setting the BN_FLG_CONSTTIME flag for nonces, failing to take a secure code path in the BN_mod_inverse method and therefore resulting in a cache-timing attack vulnerability. A malicious user with local access can recover ECDSA P-256 private keys.
In order to exploit this flaw, the attacker needs to be have local (shell) access to the machine where the message is being signed using the ECDSA algorithm with a P-256 elliptic curve key. Then using cache timing attacks (which needs precise timing), on multiple signature runs, the private key could be obtained.