OpenSSL Security Advisory

Matt Caswell matt at
Fri Jan 28 14:44:21 UTC 2022

Hash: SHA256

OpenSSL Security Advisory [28 January 2022]

BN_mod_exp may produce incorrect results on MIPS (CVE-2021-4160)

Severity: Moderate

There is a carry propagation bug in the MIPS32 and MIPS64 squaring
procedure.  Many EC algorithms are affected, including some of the
TLS 1.3 default curves.  Impact was not analyzed in detail, because the
pre-requisites for attack are considered unlikely and include reusing
private keys.  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 significant.  However,
for an attack on TLS to be meaningful, the server would have to share
the DH private key among multiple clients, which is no longer an option
since CVE-2016-0701.

This issue affects OpenSSL versions 1.0.2, 1.1.1 and 3.0.0.  It was
addressed in the releases of 1.1.1m and 3.0.1 on the 15th of December 2021. For
the 1.0.2 release it is addressed in git commit 6fc1aaaf3 that is available to
premium support customers only. It will be made available in 1.0.2zc when it is

The issue only affects OpenSSL on MIPS platforms. If that applies then:

OpenSSL 1.0.2 users should apply git commit 6fc1aaaf3 (premium support
customers only)
OpenSSL 1.1.1 users should upgrade to 1.1.1m
OpenSSL 3.0.0 users should upgrade to 3.0.1

This issue was found on the 10th of December 2021 and subsequently fixed
by Bernd Edlinger.


OpenSSL 1.0.2 is out of support and no longer receiving public updates. Extended
support is available for premium support customers:

OpenSSL 1.1.0 is out of support and no longer receiving updates of any kind.
The impact of these issues on OpenSSL 1.1.0 has not been analysed.

Users of these versions should upgrade to OpenSSL 3.0 or 1.1.1.


URL for this Security Advisory:

Note: the online version of the advisory may be updated with additional details
over time.

For details of OpenSSL severity classifications please see:


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