The security advisory for the issue can be found here: https://www.openssl.org/news/secadv_20150709.txt
OpenSSL Security Advisory [9 Jul 2015]
Alternative chains certificate forgery (CVE-2015-1793)
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
This issue was reported to OpenSSL on 24th June 2015 by Adam Langley/David Benjamin (Google/BoringSSL). The fix was developed by the BoringSSL project.
As per our previous announcements and our Release Strategy (https://www.openssl.org/about/releasestrat.html), support for OpenSSL 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.
URL for this Security Advisory: https://www.openssl.org/news/secadv_20150709.txt
Note: the online version of the advisory may be updated with additional details over time.
For details of OpenSSL severity classifications please see: https://www.openssl.org/about/secpolicy.html