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Category:   Application (VPN)  >   OpenSSL Vendors:   OpenSSL.org
(FreeBSD Issues Fix) OpenSSL Flaws Let Remote Users Deny Service and Decrypt TLS Sessions in Certain Cases
SecurityTracker Alert ID:  1035246
SecurityTracker URL:  http://securitytracker.com/id/1035246
CVE Reference:   CVE-2016-0702, CVE-2016-0703, CVE-2016-0704, CVE-2016-0705, CVE-2016-0797, CVE-2016-0798, CVE-2016-0799, CVE-2016-0800, CVE-2016-2842   (Links to External Site)
Date:  Mar 10 2016
Impact:   Denial of service via network, Disclosure of system information, Disclosure of user information, Execution of arbitrary code via network, User access via network
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): prior to versions 1.0.1s, 1.0.2g
Description:   Multiple vulnerabilities were reported in OpenSSL. A remote user can decrypt TLS sessions in certain cases. A remote user can cause denial of service conditions on the target system.

A remote user can decrypt TLS sessions in certain cases by using a server that supports SSLv2 and EXPORT cipher suites as a Bleichenbacher RSA padding oracle [CVE-2016-0800]. This attack is known as a DROWN attack.

Systems with a private key used on another server for any protocol that allows SSLv2 connections are affected.

Systems running versions prior to 1.0.2a, 1.0.1m, 1.0.0r, and 0.9.8zf (released on March 19, 2015) can be exploited more readily.

The original advisory is available at:

https://drownattack.com/drown-attack-paper.pdf

Nimrod Aviram, Sebastian Schinzel, Juraj Somorovsky, Nadia Heninger, Maik Dankel, Jens Steube, Luke Valenta, David Adrian, J. Alex Halderman, Viktor Dukhovni, Emilia Kasper, Shaanan Cohney, Susanne Engels, Christof Paar, and Yuval Shavitt reported this vulnerability.

A remote user can create a specially crafted private DSA key that, when processed by OpenSSL, will trigger a double free memory error and cause denial of service conditions [CVE-2016-0705].

Adam Langley (Google/BoringSSL) reported this vulnerability.

A remote user can supply a specially crafted username value to the target SRP server to trigger a memory leak [CVE-2016-0798].

Emilia Kasper of the OpenSSL development team reported this vulnerability.

A user can create specially crafted data (e.g., configuration file) that, when processed by OpenSSL, will trigger a null pointer dereference in the BN_hex2bn/BN_dec2bn() functions [CVE-2016-0797].

Guido Vranken reported this vulnerability.

A user can create specially crafted data that, when processed by OpenSSL, will trigger a memory error in BIO_*printf() functions [CVE-2016-0799].

Guido Vranken reported this vulnerability.

A local user can conduct a side-channel attack against a system based on the Intel Sandy-Bridge microarchitecture to potentially recover RSA keys [CVE-2016-0702].

Yuval Yarom, the University of Adelaide and NICTA, Daniel Genkin, Technion and Tel Aviv University, and Nadia Heninger, University of Pennsylvania, reported this vulnerability.

The SSLv2 's2_srvr.c' code does not ensure that a clear-key-length value is 0 for non-export ciphers. As a result, clear-key bytes can displace encrypted-key bytes, which can be exploited to conduct a key recovery attack [CVE-2016-0703].

Versions 1.0.2, 1.0.1l, 1.0.0q, and 0.9.8ze and prior versions are affected.

David Adrian and J. Alex Halderman of the University of Michigan reported this vulnerability.

The Bleichenbacher protection for export cipher suites in 's2_srvr.c' overwrites bytes incorrectly in the master-key, which may provide a Bleichenbacher oracle that can be used to decrypt sessions [CVE-2016-0704].

Versions 1.0.2, 1.0.1l, 1.0.0q, and 0.9.8ze and all prior versions are affected.

David Adrian and J. Alex Halderman of the University of Michigan reported this vulnerability.

A remote user can trigger an out-of-bounds memory write error in doapr_outch() in 'crypto/bio/b_print.c' to potentially execute arbitrary code on the target system [CVE-2016-2842].

Guido Vranken reported this vulnerability.

Impact:   A remote user can decrypt TLS sessions in certain cases.

A remote user can cause denial of service conditions.

A remote user can execute arbitrary code on the target system.

Solution:   FreeBSD has issued a fix.

The FreeBSD advisory is available at:

https://security.FreeBSD.org/advisories/FreeBSD-SA-16:12.openssl.asc

Vendor URL:  security.FreeBSD.org/advisories/FreeBSD-SA-16:12.openssl.asc (Links to External Site)
Cause:   Access control error
Underlying OS:  UNIX (FreeBSD)
Underlying OS Comments:  9.3, 10.1, 10.2

Message History:   This archive entry is a follow-up to the message listed below.
Mar 1 2016 OpenSSL Flaws Let Remote Users Deny Service and Decrypt TLS Sessions in Certain Cases



 Source Message Contents

Subject:  FreeBSD Security Advisory FreeBSD-SA-16:12.openssl

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

=============================================================================
FreeBSD-SA-16:12.openssl                                    Security Advisory
                                                          The FreeBSD Project

Topic:          Multiple OpenSSL vulnerabilities

Category:       contrib
Module:         openssl
Announced:      2016-03-10
Credits:        OpenSSL Project
Affects:        All supported versions of FreeBSD.
Corrected:      2016-03-04 00:40:15 UTC (stable/10, 10.2-BETA3)
                2016-03-03 07:30:55 UTC (releng/10.2, 10.2-RELEASE-p13)
                2016-03-03 07:30:55 UTC (releng/10.1, 10.1-RELEASE-p30)
                2016-03-10 03:58:48 UTC (stable/9, 9.3-STABLE)
                2016-03-10 10:03:28 UTC (releng/9.3, 9.3-RELEASE-p38)
CVE Name:       CVE-2016-0702, CVE-2016-0703, CVE-2016-0704, CVE-2016-0705
                CVE-2016-0797, CVE-2016-0798, CVE-2016-0799, CVE-2016-0800

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 cross-protocol attack was discovered that could lead to decryption of TLS
sessions by using a server supporting SSLv2 and EXPORT cipher suites as a
Bleichenbacher RSA padding oracle.  Note that traffic between clients and
non-vulnerable servers can be decrypted provided another server supporting
SSLv2 and EXPORT ciphers (even with a different protocol such as SMTP, IMAP
or POP3) shares the RSA keys of the non-vulnerable server.  This vulnerability
is known as DROWN.  [CVE-2016-0800]

A double free bug was discovered when OpenSSL parses malformed DSA private
keys and could lead to a DoS attack or memory corruption for applications that
receive DSA private keys from untrusted sources.  This scenario is considered
rare.  [CVE-2016-0705]

The SRP user database lookup method SRP_VBASE_get_by_user had confusing memory
management semantics; the returned pointer was sometimes newly allocated, and
sometimes owned by the callee.  The calling code has no way of distinguishing
these two cases.  [CVE-2016-0798]

In the BN_hex2bn function, the number of hex digits is calculated using an int
value |i|.  Later |bn_expand| is called with a value of |i * 4|.  For large
values of |i| this can result in |bn_expand| not allocating any memory because
|i * 4| is negative.  This can leave the internal BIGNUM data field as NULL
leading to a subsequent NULL pointer dereference.  For very large values of
|i|, the calculation |i * 4| could be a positive value smaller than |i|.  In
this case memory is allocated to the internal BIGNUM data field, but it is
insufficiently sized leading to heap corruption.  A similar issue exists in
BN_dec2bn.  This could have security consequences if BN_hex2bn/BN_dec2bn is
ever called by user applications with very large untrusted hex/dec data.  This
is anticipated to be a rare occurrence.  [CVE-2016-0797]

The internal |fmtstr| function used in processing a "%s" formatted string in
the BIO_*printf functions could overflow while calculating the length of
a string and cause an out-of-bounds read when printing very long strings.
[CVE-2016-0799]

A side-channel attack was found which makes use of cache-bank conflicts on the
Intel Sandy-Bridge microarchitecture which could lead to the recovery of RSA
keys. [CVE-2016-0702]

s2_srvr.c did not enforce that clear-key-length is 0 for non-export ciphers.
If clear-key bytes are present for these ciphers, they displace encrypted-key
bytes.  [CVE-2016-0703]

s2_srvr.c overwrites the wrong bytes in the master key when applying
Bleichenbacher protection for export cipher suites.  [CVE-2016-0704]

III. Impact

Servers that have SSLv2 protocol enabled are vulnerable to the "DROWN" attack
which allows a remote attacker to fast attack many recorded TLS connections
made to the server, even when the client did not make any SSLv2 connections
themselves.

An attacker who can supply malformed DSA private keys to OpenSSL applications
may be able to cause memory corruption which would lead to a Denial of
Service condition. [CVE-2016-0705]

An attacker connecting with an invalid username can cause memory leak, which
could eventually lead to a Denial of Service condition. [CVE-2016-0798]

An attacker who can inject malformed data into an application may be able
to cause memory corruption which would lead to a Denial of Service
condition. [CVE-2016-0797, CVE-2016-0799]

A local attacker who has control of code in a thread running on the same
hyper-threaded core as the victim thread which is performing decryptions
could recover RSA keys. [CVE-2016-0702]

An eavesdropper who can intercept SSLv2 handshake can conduct an efficient
divide-and-conquer key recovery attack and use the server as an oracle to
determine the SSLv2 master-key, using only 16 connections to the server
and negligible computation.  [CVE-2016-0703]

An attacker can use the Bleichenbacher oracle,  which enables more efficient
variant of the DROWN attack.  [CVE-2016-0704]

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 deamons using 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 deamons using 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 9.3]
# fetch https://security.FreeBSD.org/patches/SA-16:12/openssl-9.3.patch.xz
# fetch https://security.FreeBSD.org/patches/SA-16:12/openssl-9.3.patch.xz.asc
# gpg --verify openssl-9.3.patch.xz.asc

Note that the initial patch version contains a serious regression that
would lead to crash.  The following patch must be applied to address it.

# fetch https://security.FreeBSD.org/patches/SA-16:12/openssl-9.3-fix.patch
# fetch https://security.FreeBSD.org/patches/SA-16:12/openssl-9.3-fix.patch.asc
# gpg --verify openssl-9.3-fix.patch.asc

[FreeBSD 10.1]
# fetch https://security.FreeBSD.org/patches/SA-16:12/openssl-10.1.patch.xz
# fetch https://security.FreeBSD.org/patches/SA-16:12/openssl-10.1.patch.xz.asc
# gpg --verify openssl-10.1.patch.xz.asc

[FreeBSD 10.2]
# fetch https://security.FreeBSD.org/patches/SA-16:12/openssl-10.2.patch
# fetch https://security.FreeBSD.org/patches/SA-16:12/openssl-10.2.patch.asc
# gpg --verify openssl-10.2.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 deamons using 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/                                                         r296598
releng/9.3/                                                       r296611
stable/10/                                                        r296371
releng/10.1/                                                      r296341
releng/10.2/                                                      r296341
- -------------------------------------------------------------------------

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/20160301.txt>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-0702>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-0703>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-0704>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-0705>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-0797>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-0798>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-0799>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-0800>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:12.openssl.asc>
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