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Category:   Application (VPN)  >   OpenSSL Vendors:   OpenSSL.org
(FreeBSD Issues Fix) OpenSSL DSA Signing Constant Timing Bug May Let Remote Users Obtain Potentially Sensitive Information on the Target System
SecurityTracker Alert ID:  1036889
SecurityTracker URL:  http://securitytracker.com/id/1036889
CVE Reference:   CVE-2016-2178   (Links to External Site)
Date:  Sep 23 2016
Impact:   Disclosure of authentication information, Disclosure of system 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.

The DSA signing algorithm may fail to run in constant time when the BN_FLG_CONSTTIME flag is set. A remote user may be able to exploit this to obtain potentially sensitive timing information regarding the cryptographic signature process, including the DSA private key.

The original advisory is available at:

http://eprint.iacr.org/2016/594.pdf

Cesar Pereida (Aalto University), Billy Brumley (Tampere University of Technology), and Yuval Yarom (The University of Adelaide and NICTA) reported this vulnerability.

Impact:   A remote user can obtain potentially sensitive timing information regarding the cryptographic signature process, including the DSA private key.
Solution:   FreeBSD has issued a fix.

The FreeBSD advisory is available at:

https://security.FreeBSD.org/advisories/FreeBSD-SA-16:26.openssl.asc

Vendor URL:  security.FreeBSD.org/advisories/FreeBSD-SA-16:26.openssl.asc (Links to External Site)
Cause:   State error
Underlying OS:  UNIX (FreeBSD)
Underlying OS Comments:  9.3, 10.1, 10.2, 10.3, 11.0

Message History:   This archive entry is a follow-up to the message listed below.
Jun 8 2016 OpenSSL DSA Signing Constant Timing Bug May Let Remote Users Obtain Potentially Sensitive Information on the Target System



 Source Message Contents

Subject:  FreeBSD Security Advisory FreeBSD-SA-16:26.openssl

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

=============================================================================
FreeBSD-SA-16:26.openssl                                    Security Advisory
                                                          The FreeBSD Project

Topic:          Multiple OpenSSL vulnerabilities

Category:       contrib
Module:         openssl
Announced:      2016-09-23
Credits:        OpenSSL Project
Affects:        All supported versions of FreeBSD.
Corrected:      2016-09-22 14:57:48 UTC (stable/11, 11.0-STABLE)
                2016-09-22 15:55:27 UTC (releng/11.0, 11.0-RELEASE)
                2016-09-22 15:05:38 UTC (stable/10, 10.3-STABLE)
                2016-09-23 07:48:34 UTC (releng/10.3, 10.3-RELEASE-p8)
                2016-09-23 07:48:34 UTC (releng/10.2, 10.2-RELEASE-p21)
                2016-09-23 07:48:34 UTC (releng/10.1, 10.1-RELEASE-p38)
                2016-09-23 07:44:10 UTC (stable/9, 9.3-STABLE)
                2016-09-23 07:48:34 UTC (releng/9.3, 9.3-RELEASE-p46)
CVE Name:       CVE-2016-2177, CVE-2016-2178, CVE-2016-2179, CVE-2016-2180,
                CVE-2016-2181, CVE-2016-2182, CVE-2016-6302, CVE-2016-6303,
                CVE-2016-6304, CVE-2016-6306

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

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 implementing the Secure Sockets Layer (SSL v2/v3)
and Transport Layer Security (TLS v1) protocols as well as a full-strength
general purpose cryptography library.

II.  Problem Description

A malicious client can send an excessively large OCSP Status Request extension.
If that client continually requests renegotiation, sending a large OCSP Status
Request extension each time, then there will be unbounded memory growth on the
server. [CVE-2016-6304]

An overflow can occur in MDC2_Update() either if called directly or through
the EVP_DigestUpdate() function using MDC2. If an attacker is able to supply
very large amounts of input data after a previous call to EVP_EncryptUpdate()
with a partial block then a length check can overflow resulting in a heap
corruption. [CVE-2016-6303]

If a server uses SHA512 for TLS session ticket HMAC it is vulnerable to a
DoS attack where a malformed ticket will result in an OOB read which will
ultimately crash. [CVE-2016-6302]

The function BN_bn2dec() does not check the return value of BN_div_word().
This can cause an OOB write if an application uses this function with an
overly large BIGNUM. This could be a problem if an overly large certificate
or CRL is printed out from an untrusted source. TLS is not affected because
record limits will reject an oversized certificate before it is parsed.
[CVE-2016-2182]

The function TS_OBJ_print_bio() misuses OBJ_obj2txt(): the return value is
the total length the OID text representation would use and not the amount
of data written. This will result in OOB reads when large OIDs are presented.
[CVE-2016-2180]

Some calculations of limits in OpenSSL have used undefined pointer arithmetic. 
This could cause problems with some malloc implementations. [CVE-2016-2177]

Operations in the DSA signing algorithm should run in constant time in order to
avoid side channel attacks. A flaw in the OpenSSL DSA implementation means that
a non-constant time codepath is followed for certain operations. [CVE-2016-2178]

In a DTLS connection where handshake messages are delivered out-of-order those
messages that OpenSSL is not yet ready to process will be buffered for later
use. Under certain circumstances, a flaw in the logic means that those messages
do not get removed from the buffer even though the handshake has been completed.
An attacker could force up to approx. 15 messages to remain in the buffer when
they are no longer required. These messages will be cleared when the DTLS
connection is closed. The default maximum size for a message is 100k. Therefore
the attacker could force an additional 1500k to be consumed per connection.
[CVE-2016-2179]

A flaw in the DTLS replay attack protection mechanism means that records that
arrive for future epochs update the replay protection "window" before the MAC
for the record has been validated. This could be exploited by an attacker by
sending a record for the next epoch (which does not have to decrypt or have a
valid MAC), with a very large sequence number. This means that all subsequent
legitimate packets are dropped causing a denial of service for a specific
DTLS connection. [CVE-2016-2181]

In OpenSSL 1.0.2 and earlier some missing message length checks can result in
OOB reads of up to 2 bytes beyond an allocated buffer. There is a theoretical
DoS risk but this has not been observed in practice on common platforms.
[CVE-2016-6306]

III. Impact

A remote attacker can cause OpenSSL server, regardless whether OCSP is supported,
to have unbounded memory growth, and eventually lead to a Denial of Service.
[CVE-2016-6304]

If an attacker is able to supply very large amounts of input data after a previous
call to EVP_EncryptUpdate() with a partial block then a length check can overflow
resulting in a heap corruption. [CVE-2016-6303]

An attacker who can send a malformed ticket to the server can cause an OOB read
which will ultimately lead to a crash, resulting in a Denial of Service.
[CVE-2016-6302]

A local attacker can cause an application that parses overly large certificate or
CRL to crash.  TLS is not affected. [CVE-2016-2182]

A local attacker who can create a specially-crafted time stamp file and pass it
through the "ts" command of openssl(1) can cause it to crash.  This functionality
is not used by the SSL/TLS implementation. [CVE-2016-2180]

Some OpenSSL code is questionable to integer overflow, which may lead to heap
corruption. [CVE-2016-2177]

An attacker may recover the private DSA key by conducting timing attack.
[CVE-2016-2178]

A remote attacker may cause a DTLS server to exhaust memory, resulting in a
Denial of Service. [CVE-2016-2179]

A remote attacker who can send DTLS records can cause the server to drop all
subsequent packets for a specific connection. [CVE-2016-2181]

A remote attacker can, in theory, cause OOB reads if the server enabled client
authentication. [CVE-2016-6306]

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 https://security.FreeBSD.org/patches/SA-16:26/openssl-10.3.patch
# fetch https://security.FreeBSD.org/patches/SA-16:26/openssl-10.3.patch.asc
# gpg --verify openssl-10.3.patch.asc

[FreeBSD 10.1 and 10.2]
# fetch https://security.FreeBSD.org/patches/SA-16:26/openssl-10.2.patch
# fetch https://security.FreeBSD.org/patches/SA-16:26/openssl-10.2.patch.as
# gpg --verify openssl-10.2.patch.asc

[FreeBSD 9.3]
# fetch https://security.FreeBSD.org/patches/SA-16:26/openssl-9.3.patch
# fetch https://security.FreeBSD.org/patches/SA-16:26/openssl-9.3.patch.as
# gpg --verify openssl-9.3.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:https://www.FreeBSD.org/handbook/makeworld.html>.

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/9/                                                         r306229
releng/9.3/                                                       r206230
stable/10/                                                        r306196
releng/10.1/                                                      r206230
releng/10.2/                                                      r206230
releng/10.3/                                                      r206230
stable/11/                                                        r306195
releng/11.0/                                                      r306198
- -------------------------------------------------------------------------

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://svn.freebsd.org/base

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

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://www.openssl.org/news/secadv/20160922.txt>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-2177>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-2178>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-2179>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-2180>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-2181>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-2182>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-6302>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-6303>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-6304>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-6306>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:26.openssl.asc>
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