There is a carry propagating bug in the x86_64 Montgomery squaring
procedure in OpenSSL before 1.0.2m and 1.1.0 before 1.1.0g. 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. This only affects processors that support the
BMI1, BMI2 and ADX extensions like Intel Broadwell (5th generation) and
later or AMD Ryzen.

mdeslaur