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. References: http://seclists.org/oss-sec/2017/q1/52 http://eprint.iacr.org/2016/1195 Fix available at: https://git.openssl.org/?p=openssl.git;a=commit;h=f54be179aa4cbbd944728771d7d59ed588158a12
