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OpenSSL Security Advisory [22 Sep 2016]
========================================

OCSP Status Request extension unbounded memory growth (CVE-2016-6304)
=====================================================================

Severity: High

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. This will eventually lead to a Denial Of Service attack through memory
exhaustion. Servers with a default configuration are vulnerable even if they do
not support OCSP. Builds using the "no-ocsp" build time option are not affected.

Servers using OpenSSL versions prior to 1.0.1g are not vulnerable in a default
configuration, instead only if an application explicitly enables OCSP stapling
support.

OpenSSL 1.1.0 users should upgrade to 1.1.0a
OpenSSL 1.0.2 users should upgrade to 1.0.2i
OpenSSL 1.0.1 users should upgrade to 1.0.1u

This issue was reported to OpenSSL on 29th August 2016 by Shi Lei (Gear Team,
Qihoo 360 Inc.). The fix was developed by Matt Caswell of the OpenSSL
development team.

SSL_peek() hang on empty record (CVE-2016-6305)
===============================================

Severity: Moderate

OpenSSL 1.1.0 SSL/TLS will hang during a call to SSL_peek() if the peer sends an
empty record. This could be exploited by a malicious peer in a Denial Of Service
attack.

OpenSSL 1.1.0 users should upgrade to 1.1.0a

This issue was reported to OpenSSL on 10th September 2016 by Alex Gaynor. The
fix was developed by Matt Caswell of the OpenSSL development team.

SWEET32 Mitigation (CVE-2016-2183)
==================================

Severity: Low

SWEET32 (https://sweet32.info) is an attack on older block cipher algorithms
that use a block size of 64 bits. In mitigation for the SWEET32 attack DES based
ciphersuites have been moved from the HIGH cipherstring group to MEDIUM in
OpenSSL 1.0.1 and OpenSSL 1.0.2.  OpenSSL 1.1.0 since release has had these
ciphersuites disabled by default.

OpenSSL 1.0.2 users should upgrade to 1.0.2i
OpenSSL 1.0.1 users should upgrade to 1.0.1u

This issue was reported to OpenSSL on 16th August 2016 by Karthikeyan
Bhargavan and Gaetan Leurent (INRIA). The fix was developed by Rich Salz of the
OpenSSL development team.

OOB write in MDC2_Update() (CVE-2016-6303)
==========================================

Severity: Low

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.

The amount of data needed is comparable to SIZE_MAX which is impractical
on most platforms.

OpenSSL 1.0.2 users should upgrade to 1.0.2i
OpenSSL 1.0.1 users should upgrade to 1.0.1u

This issue was reported to OpenSSL on 11th August 2016 by Shi Lei (Gear Team,
Qihoo 360 Inc.). The fix was developed by Stephen Henson of the OpenSSL
development team.

Malformed SHA512 ticket DoS (CVE-2016-6302)
===========================================

Severity: Low

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.

The use of SHA512 in TLS session tickets is comparatively rare as it requires
a custom server callback and ticket lookup mechanism.

OpenSSL 1.0.2 users should upgrade to 1.0.2i
OpenSSL 1.0.1 users should upgrade to 1.0.1u

This issue was reported to OpenSSL on 19th August 2016 by Shi Lei (Gear Team,
Qihoo 360 Inc.). The fix was developed by Stephen Henson of the OpenSSL
development team.

OOB write in BN_bn2dec() (CVE-2016-2182)
========================================

Severity: Low

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.

OpenSSL 1.0.2 users should upgrade to 1.0.2i
OpenSSL 1.0.1 users should upgrade to 1.0.1u

This issue was reported to OpenSSL on 2nd August 2016 by Shi Lei (Gear Team,
Qihoo 360 Inc.). The fix was developed by Stephen Henson of the OpenSSL
development team.

OOB read in TS_OBJ_print_bio() (CVE-2016-2180)
==============================================

Severity: Low

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.

OpenSSL 1.0.2 users should upgrade to 1.0.2i
OpenSSL 1.0.1 users should upgrade to 1.0.1u

This issue was reported to OpenSSL on 21st July 2016 by Shi Lei (Gear Team,
Qihoo 360 Inc.). The fix was developed by Stephen Henson of the OpenSSL
development team.

Pointer arithmetic undefined behaviour (CVE-2016-2177)
======================================================

Severity: Low

Avoid some undefined pointer arithmetic

A common idiom in the codebase is to check limits in the following manner:
"p + len > limit"

Where "p" points to some malloc'd data of SIZE bytes and
limit == p + SIZE

"len" here could be from some externally supplied data (e.g. from a TLS
message).

The rules of C pointer arithmetic are such that "p + len" is only well
defined where len <= SIZE. Therefore the above idiom is actually
undefined behaviour.

For example this could cause problems if some malloc implementation
provides an address for "p" such that "p + len" actually overflows for
values of len that are too big and therefore p + len < limit.

OpenSSL 1.0.2 users should upgrade to 1.0.2i
OpenSSL 1.0.1 users should upgrade to 1.0.1u

This issue was reported to OpenSSL on 4th May 2016 by Guido Vranken. The
fix was developed by Matt Caswell of the OpenSSL development team.

Constant time flag not preserved in DSA signing (CVE-2016-2178)
===============================================================

Severity: Low

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. This has been
demonstrated through a cache-timing attack to be sufficient for an attacker to
recover the private DSA key.

OpenSSL 1.0.2 users should upgrade to 1.0.2i
OpenSSL 1.0.1 users should upgrade to 1.0.1u

This issue was reported to OpenSSL on 23rd May 2016 by César Pereida (Aalto
University), Billy Brumley (Tampere University of Technology), and Yuval Yarom
(The University of Adelaide and NICTA). The fix was developed by César Pereida.

DTLS buffered message DoS (CVE-2016-2179)
=========================================

Severity: Low

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. By
opening many simulataneous connections an attacker could cause a DoS attack
through memory exhaustion.

OpenSSL 1.0.2 DTLS users should upgrade to 1.0.2i
OpenSSL 1.0.1 DTLS users should upgrade to 1.0.1u

This issue was reported to OpenSSL on 22nd June 2016 by Quan Luo. The fix was
developed by Matt Caswell of the OpenSSL development team.

DTLS replay protection DoS (CVE-2016-2181)
==========================================

Severity: Low

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.

OpenSSL 1.0.2 DTLS users should upgrade to 1.0.2i
OpenSSL 1.0.1 DTLS users should upgrade to 1.0.1u

This issue was reported to OpenSSL on 21st November 2015 by the OCAP audit team.
The fix was developed by Matt Caswell of the OpenSSL development team.

Certificate message OOB reads (CVE-2016-6306)
=============================================

Severity: Low

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.

The messages affected are client certificate, client certificate request and
server certificate. As a result the attack can only be performed against
a client or a server which enables client authentication.

OpenSSL 1.1.0 is not affected.

OpenSSL 1.0.2 users should upgrade to 1.0.2i
OpenSSL 1.0.1 users should upgrade to 1.0.1u

This issue was reported to OpenSSL on 22nd August 2016 by Shi Lei (Gear Team,
Qihoo 360 Inc.). The fix was developed by Stephen Henson of the OpenSSL
development team.

Excessive allocation of memory in tls_get_message_header() (CVE-2016-6307)
==========================================================================

Severity: Low

A TLS message includes 3 bytes for its length in the header for the message.
This would allow for messages up to 16Mb in length. Messages of this length are
excessive and OpenSSL includes a check to ensure that a peer is sending
reasonably sized messages in order to avoid too much memory being consumed to
service a connection. A flaw in the logic of version 1.1.0 means that memory for
the message is allocated too early, prior to the excessive message length
check. Due to way memory is allocated in OpenSSL this could mean an attacker
could force up to 21Mb to be allocated to service a connection. This could lead
to a Denial of Service through memory exhaustion. However, the excessive message
length check still takes place, and this would cause the connection to
immediately fail. Assuming that the application calls SSL_free() on the failed
conneciton in a timely manner then the 21Mb of allocated memory will then be
immediately freed again. Therefore the excessive memory allocation will be
transitory in nature. This then means that there is only a security impact if:

1) The application does not call SSL_free() in a timely manner in the
event that the connection fails
or
2) The application is working in a constrained environment where there
is very little free memory
or
3) The attacker initiates multiple connection attempts such that there
are multiple connections in a state where memory has been allocated for
the connection; SSL_free() has not yet been called; and there is
insufficient memory to service the multiple requests.

Except in the instance of (1) above any Denial Of Service is likely to
be transitory because as soon as the connection fails the memory is
subsequently freed again in the SSL_free() call. However there is an
increased risk during this period of application crashes due to the lack
of memory - which would then mean a more serious Denial of Service.

This issue does not affect DTLS users.

OpenSSL 1.1.0 TLS users should upgrade to 1.1.0a

This issue was reported to OpenSSL on 18th September 2016 by Shi Lei (Gear Team,
Qihoo 360 Inc.). The fix was developed by Matt Caswell of the OpenSSL
development team.

Excessive allocation of memory in dtls1_preprocess_fragment() (CVE-2016-6308)
=============================================================================

Severity: Low

This issue is very similar to CVE-2016-6307. The underlying defect is different
but the security analysis and impacts are the same except that it impacts DTLS.

A DTLS message includes 3 bytes for its length in the header for the message.
This would allow for messages up to 16Mb in length. Messages of this length are
excessive and OpenSSL includes a check to ensure that a peer is sending
reasonably sized messages in order to avoid too much memory being consumed to
service a connection. A flaw in the logic of version 1.1.0 means that memory for
the message is allocated too early, prior to the excessive message length
check. Due to way memory is allocated in OpenSSL this could mean an attacker
could force up to 21Mb to be allocated to service a connection. This could lead
to a Denial of Service through memory exhaustion. However, the excessive message
length check still takes place, and this would cause the connection to
immediately fail. Assuming that the application calls SSL_free() on the failed
conneciton in a timely manner then the 21Mb of allocated memory will then be
immediately freed again. Therefore the excessive memory allocation will be
transitory in nature. This then means that there is only a security impact if:

1) The application does not call SSL_free() in a timely manner in the
event that the connection fails
or
2) The application is working in a constrained environment where there
is very little free memory
or
3) The attacker initiates multiple connection attempts such that there
are multiple connections in a state where memory has been allocated for
the connection; SSL_free() has not yet been called; and there is
insufficient memory to service the multiple requests.

Except in the instance of (1) above any Denial Of Service is likely to
be transitory because as soon as the connection fails the memory is
subsequently freed again in the SSL_free() call. However there is an
increased risk during this period of application crashes due to the lack
of memory - which would then mean a more serious Denial of Service.

This issue does not affect TLS users.

OpenSSL 1.1.0 DTLS users should upgrade to 1.1.0a

This issue was reported to OpenSSL on 18th September 2016 by Shi Lei (Gear Team,
Qihoo 360 Inc.). The fix was developed by Matt Caswell of the OpenSSL
development team.

Note
====

As per our previous announcements and our Release Strategy
(https://www.openssl.org/policies/releasestrat.html), support for OpenSSL
version 1.0.1 will cease on 31st December 2016. No security updates for that
version will be provided after that date. Users of 1.0.1 are advised to
upgrade.

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/20160922.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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