[openssl-users] OpenSSL Security Advisory

Thu Dec 7 13:59:08 UTC 2017

OpenSSL 1.0.2 (starting from version 1.0.2b) introduced an "error state"
mechanism. The intent was that if a fatal error occurred during a handshake then
OpenSSL would move into the error state and would immediately fail if you
attempted to continue the handshake. This works as designed for the explicit
handshake functions (SSL_do_handshake(), SSL_accept() and SSL_connect()),
however due to a bug it does not work correctly if SSL_read() or SSL_write() is
called directly. In that scenario, if the handshake fails then a fatal error
will be returned in the initial function call. If SSL_read()/SSL_write() is
subsequently called by the application for the same SSL object then it will
succeed and the data is passed without being decrypted/encrypted directly from
the SSL/TLS record layer.

In order to exploit this issue an application bug would have to be present that
resulted in a call to SSL_read()/SSL_write() being issued after having already
received a fatal error.

This issue does not affect OpenSSL 1.1.0.

OpenSSL 1.0.2 users should upgrade to 1.0.2n

This issue was reported to OpenSSL on 10th November 2017 by David Benjamin
(Google). The fix was proposed by David Benjamin and implemented by Matt Caswell
of the OpenSSL development team.

rsaz_1024_mul_avx2 overflow bug on x86_64 (CVE-2017-3738)
=========================================================

Severity: Low

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.

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.

OpenSSL 1.0.2 users should upgrade to 1.0.2n

This issue was reported to OpenSSL on 22nd November 2017 by David Benjamin
(Google). The issue was originally found via the OSS-Fuzz project. The fix was
developed by Andy Polyakov of the OpenSSL development team.

Note
====

Support for version 1.0.1 ended on 31st December 2016. Support for versions
0.9.8 and 1.0.0 ended on 31st December 2015. Those versions are no longer
receiving security updates.

References
==========

URL for this Security Advisory:
https://www.openssl.org/news/secadv/20171207.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/policies/secpolicy.html
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