OpenSSL Vulnerability: Certificate Check Bypass
New vulnerability has been discovered in openSSL with a high severity level. On 24th June 2015 Adam Langley/David Benjamin (Google/BoringSSL) reoprted that, during certificate verification, OpenSSL (starting from version 1.0.1n and 1.0.2b) will attempt to find an alternative certificate chain if the first attempt to build such a chain fails. An error in the implementation of this logic can mean that an attacker could cause certain checks on untrusted certificates to be bypassed, such as the CA flag, enabling them to use a valid leaf certificate to act as a CA and “issue” an invalid certificate.
This issue will impact any application that verifies certificates including SSL/TLS/DTLS clients and SSL/TLS/DTLS servers using client authentication. This issue affects OpenSSL versions 1.0.2c, 1.0.2b, 1.0.1n and 1.0.1o. OpenSSL 1.0.2b/1.0.2c users should upgrade to 1.0.2d OpenSSL 1.0.1n/1.0.1o users should upgrade to 1.0.1p.
According to OpenSSL, support for versions 1.0.0 and 0.9.8 will cease on 31st December 2015. No security updates for these releases will be provided after that date. Users of these releases are advised to upgrade.