OpenSSL X509_cmp_time DoS

August 28, 2015

After receiving the certificate(either from client to server or server to client) OpenSSL calls X509_cmp_time to perform various checks on the certificate including comparison of notBefore and notAfter validity times against the current time. The function allocates buffer to store bytes in VisibleString. The malformed VisibleString can lead to a read read-access violation, which leads to termination of application

Using crafted certificate with malformed UTCTime or GeneralizedTime field Remote attacker can exploit this vulnerability causing denial of service.

Dell SonicWALL has released an IPS signature to detect and block exploitation attempts targeting this vulnerability. The signature is listed below:

  • 11109 OpenSSL X509 DoS
  • 11110 OpenSSL X509 DoS 1

The vulnerability is referred by CVE as CVE-2015-1789.