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Category:   Application (VPN)  >   OpenSSL Vendors:
(FreeBSD Issues Fix) OpenSSL bn_sqrx8x_internal() Carry Bug Lets Remote Users Obtain Potentially Sensitive Information on the Target System in Certain Cases
SecurityTracker Alert ID:  1039894
SecurityTracker URL:
CVE Reference:   CVE-2017-3736   (Links to External Site)
Date:  Nov 29 2017
Impact:   Disclosure of authentication information
Fix Available:  Yes  Vendor Confirmed:  Yes  

Description:   A vulnerability was reported in OpenSSL. A remote user can obtain potentially sensitive information on the target system in certain cases.

A remote user can exploit a carry propagation flaw in the the x86_64 Montgomery squaring function bn_sqrx8x_internal() to potentially determine information about the private key in certain situations.

Processors that support the BMI1, BMI2, and ADX extensions (e.g., Intel Broadwell 5th generation and later, AMD Ryzen) are affected.

EC algorithms are not affected.

The Google OSS-Fuzz project reported this vulnerability.

Impact:   A remote user can potentially determine information about the private key in certain situations.
Solution:   FreeBSD has issued a fix.

The FreeBSD advisory is available at:

Vendor URL: (Links to External Site)
Cause:   State error
Underlying OS:  UNIX (FreeBSD)
Underlying OS Comments:  10.3, 10.4, 11.0, 11.1

Message History:   This archive entry is a follow-up to the message listed below.
Nov 2 2017 OpenSSL bn_sqrx8x_internal() Carry Bug Lets Remote Users Obtain Potentially Sensitive Information on the Target System in Certain Cases

 Source Message Contents

Subject:  FreeBSD Security Advisory FreeBSD-SA-17:11.openssl

Hash: SHA512

FreeBSD-SA-17:11.openssl                                    Security Advisory
                                                          The FreeBSD Project

Topic:          OpenSSL multiple vulnerabilities

Category:       contrib
Module:         openssl
Announced:      2017-11-29
Affects:        All supported versions of FreeBSD.
Corrected:      2017-11-02 18:30:41 UTC (stable/11, 11.1-STABLE)
                2017-11-29 05:59:12 UTC (releng/11.1, 11.1-RELEASE-p5)
                2017-11-29 05:59:12 UTC (releng/11.0, 11.0-RELEASE-p16)
                2017-11-29 05:35:28 UTC (stable/10, 10.4-STABLE)
                2017-11-29 05:59:50 UTC (releng/10.4, 10.4-RELEASE-p4)
                2017-11-29 05:59:50 UTC (releng/10.3, 10.3-RELEASE-p25)
CVE Name:       CVE-2017-3735, CVE-2017-3736

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:>.

I.   Background

FreeBSD includes software from the OpenSSL Project.  The OpenSSL Project is
a collaborative effort to develop a robust, commercial-grade, full-featured
Open Source toolkit for the Transport Layer Security (TLS) and Secure Sockets
Layer (SSL) protocols. It is also a full-strength general purpose
cryptography library.

II.  Problem Description

If an X.509 certificate has a malformed IPAddressFamily extension, OpenSSL
could do a one-byte buffer overread. [CVE-2017-3735]

There is a carry propagating bug in the x86_64 Montgomery squaring procedure.
This only affects processors that support the BMI1, BMI2 and ADX extensions
like Intel Broadwell (5th generation) and later or AMD Ryzen. [CVE-2017-3736]
This bug only affects FreeBSD 11.x.

III. Impact

Application using OpenSSL may display erroneous certificate in text format.

Mishandling of carry propagation will produce incorrect output, and make it
easier for a remote attacker to obtain sensitive private-key information.
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. [CVE-2017-3736]

IV.  Workaround

No workaround is available.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date.

Restart all daemons that use the library, or reboot the system.

2) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

Restart all daemons that use the library, or reboot the system.

3) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

[FreeBSD 10.3]
# fetch
# fetch
# gpg --verify openssl-10.patch.asc

[FreeBSD 11.x]
# fetch
# fetch
# gpg --verify openssl.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile the operating system using buildworld and installworld as
described in <URL:>.

Restart all daemons that use the library, or reboot the system.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/10/                                                        r326357
releng/10.3/                                                      r326359
releng/10.4/                                                      r326359
stable/11/                                                        r325337
releng/11.0/                                                      r326358
releng/11.1/                                                      r326358
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://

Or visit the following URL, replacing NNNNNN with the revision number:


VII. References




The latest revision of this advisory is available at
Version: GnuPG v2.2.3 (FreeBSD)

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