CVE-2017-3738

There is an overflow bug in the AVX2 Montgomery multiplication procedure
used in exponentiation with 1024-bit moduli. 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 DH1024 are considered just feasible, 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
significant. However, for an attack on TLS to be meaningful, the server
would have to share the DH1024 private key among multiple clients, which is
no longer an option since CVE-2016-0701. This only affects processors that
support the AVX2 but not ADX extensions like Intel Haswell (4th
generation). Note: The impact from this issue is similar to CVE-2017-3736,
CVE-2017-3732 and CVE-2015-3193. OpenSSL version 1.0.2-1.0.2m and
1.1.0-1.1.0g are affected. Fixed in OpenSSL 1.0.2n. Due to the low severity
of this issue we are not issuing a new release of OpenSSL 1.1.0 at this
time. The fix will be included in OpenSSL 1.1.0h when it becomes available.
The fix is also available in commit e502cc86d in the OpenSSL git
repository.

Notes