Quoting form the OpenSSL upstream advisory:

Montgomery multiplication may produce incorrect results (CVE-2016-7055)
=======================================================================

Severity: Low

There is a carry propagating bug in the Broadwell-specific Montgomery
multiplication procedure that handles input lengths divisible by, but
longer than 256 bits. Analysis suggests that attacks against RSA, DSA
and DH private keys are impossible. This is because the subroutine in
question is not used in operations with the private key itself and an input
of the attacker's direct choice. Otherwise the bug can manifest itself as
transient authentication and key negotiation failures or reproducible
erroneous outcome of public-key operations with specially crafted input.
Among EC algorithms only Brainpool P-512 curves are affected and one
presumably can attack ECDH key negotiation. Impact was not analyzed in
detail, because pre-requisites for attack are considered unlikely. Namely
multiple clients have to choose the curve in question and the server has to
share the private key among them, neither of which is default behaviour.
Even then only clients that chose the curve will be affected.

OpenSSL 1.1.0 users should upgrade to 1.1.0c

This issue does not affect OpenSSL versions prior to 1.0.2. Due to the low
severity of this defect we are not issuing a new 1.0.2 release at this time.
We recommend that 1.0.2 users wait for the next 1.0.2 release for the fix to
become available. The fix is also available in the OpenSSL git repository in
commit 57c4b9f6a2.

This issue was publicly reported as transient failures and was not
initially recognized as a security issue. Thanks to Richard Morgan for
providing reproducible case. The fix was developed by Andy Polyakov of
the OpenSSL development team.

https://www.openssl.org/news/secadv/20161110.txt