The following was reported by OpenSSL upstream: There is a carry propagating bug in the x86_64 Montgomery squaring procedure. No EC algorithms are affected. Analysis suggests that attacks against RSA and DSA as a result of this defect would be very difficult to perform and are not believed likely. Attacks against DH are considered just feasible (although very difficult) because most of the work necessary to deduce information about a private key may be performed offline. The amount of resources required for such an attack would be very significant and likely only accessible to a limited number of attackers. An attacker would additionally need online access to an unpatched system using the target private key in a scenario with persistent DH parameters and a private key that is shared between multiple clients. For example this can occur by default in OpenSSL DHE based SSL/TLS ciphersuites. This issue affects OpenSSL version 1.0.2. OpenSSL 1.0.2 users should upgrade to 1.0.2e This issue was reported to OpenSSL on August 13 2015 by Hanno Böck. The fix was developed by Andy Polyakov of the OpenSSL development team.
External References: https://openssl.org/news/secadv/20151203.txt
Upstream commits: OpenSSL 1.0.2: https://git.openssl.org/?p=openssl.git;a=commit;h=d73cc256c8e256c32ed959456101b73ba9842f72
openssl-1.0.2e-1.fc23 has been pushed to the Fedora 23 stable repository. If problems still persist, please make note of it in this bug report.
Statement: This issue does not affect the version of OpenSSL as shipped with Red Hat Enterprise Linux 5, 6 and 7.