The asn1_time_to_time_t function in ext/openssl/openssl.c in PHP before 5.3.28, 5.4.x before 5.4.23, and 5.5.x before 5.5.7 does not properly parse notBefore and notAfter timestamps in X.509 certificates, which allows remote attackers to execute arbitrary code or cause a denial of service via a crafted certificate that is not properly handled by the openssl_x509_parse function.