TLS/SSL and crypto library
00a4c14214
DTLS can handle out of order record delivery. Additionally since handshake messages can be bigger than will fit into a single packet, the messages can be fragmented across multiple records (as with normal TLS). That means that the messages can arrive mixed up, and we have to reassemble them. We keep a queue of buffered messages that are "from the future", i.e. messages we're not ready to deal with yet but have arrived early. The messages held there may not be full yet - they could be one or more fragments that are still in the process of being reassembled. The code assumes that we will eventually complete the reassembly and when that occurs the complete message is removed from the queue at the point that we need to use it. However, DTLS is also tolerant of packet loss. To get around that DTLS messages can be retransmitted. If we receive a full (non-fragmented) message from the peer after previously having received a fragment of that message, then we ignore the message in the queue and just use the non-fragmented version. At that point the queued message will never get removed. Additionally the peer could send "future" messages that we never get to in order to complete the handshake. Each message has a sequence number (starting from 0). We will accept a message fragment for the current message sequence number, or for any sequence up to 10 into the future. However if the Finished message has a sequence number of 2, anything greater than that in the queue is just left there. So, in those two ways we can end up with "orphaned" data in the queue that will never get removed - except when the connection is closed. At that point all the queues are flushed. An attacker could seek to exploit this by filling up the queues with lots of large messages that are never going to be used in order to attempt a DoS by memory exhaustion. I will assume that we are only concerned with servers here. It does not seem reasonable to be concerned about a memory exhaustion attack on a client. They are unlikely to process enough connections for this to be an issue. A "long" handshake with many messages might be 5 messages long (in the incoming direction), e.g. ClientHello, Certificate, ClientKeyExchange, CertificateVerify, Finished. So this would be message sequence numbers 0 to 4. Additionally we can buffer up to 10 messages in the future. Therefore the maximum number of messages that an attacker could send that could get orphaned would typically be 15. The maximum size that a DTLS message is allowed to be is defined by max_cert_list, which by default is 100k. Therefore the maximum amount of "orphaned" memory per connection is 1500k. Message sequence numbers get reset after the Finished message, so renegotiation will not extend the maximum number of messages that can be orphaned per connection. As noted above, the queues do get cleared when the connection is closed. Therefore in order to mount an effective attack, an attacker would have to open many simultaneous connections. Issue reported by Quan Luo. CVE-2016-2179 Reviewed-by: Richard Levitte <levitte@openssl.org> |
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OpenSSL 1.0.1u-dev
Copyright (c) 1998-2015 The OpenSSL Project
Copyright (c) 1995-1998 Eric A. Young, Tim J. Hudson
All rights reserved.
DESCRIPTION
-----------
The OpenSSL Project is a collaborative effort to develop a robust,
commercial-grade, fully featured, and Open Source toolkit implementing the
Secure Sockets Layer (SSLv3) and Transport Layer Security (TLS) protocols as
well as a full-strength general purpose cryptograpic library. The project is
managed by a worldwide community of volunteers that use the Internet to
communicate, plan, and develop the OpenSSL toolkit and its related
documentation.
OpenSSL is descended from the SSLeay library developed by Eric A. Young
and Tim J. Hudson. The OpenSSL toolkit is licensed under a dual-license (the
OpenSSL license plus the SSLeay license), which means that you are free to
get and use it for commercial and non-commercial purposes as long as you
fulfill the conditions of both licenses.
OVERVIEW
--------
The OpenSSL toolkit includes:
libssl.a:
Provides the client and server-side implementations for SSLv3 and TLS.
libcrypto.a:
Provides general cryptographic and X.509 support needed by SSL/TLS but
not logically part of it.
openssl:
A command line tool that can be used for:
Creation of key parameters
Creation of X.509 certificates, CSRs and CRLs
Calculation of message digests
Encryption and decryption
SSL/TLS client and server tests
Handling of S/MIME signed or encrypted mail
And more...
INSTALLATION
------------
See the appropriate file:
INSTALL Linux, Unix, etc.
INSTALL.DJGPP DOS platform with DJGPP
INSTALL.NW Netware
INSTALL.OS2 OS/2
INSTALL.VMS VMS
INSTALL.W32 Windows (32bit)
INSTALL.W64 Windows (64bit)
INSTALL.WCE Windows CE
SUPPORT
-------
See the OpenSSL website www.openssl.org for details on how to obtain
commercial technical support.
If you have any problems with OpenSSL then please take the following steps
first:
- Download the current snapshot from ftp://ftp.openssl.org/snapshot/
to see if the problem has already been addressed
- Remove ASM versions of libraries
- Remove compiler optimisation flags
If you wish to report a bug then please include the following information in
any bug report:
- On Unix systems:
Self-test report generated by 'make report'
- On other systems:
OpenSSL version: output of 'openssl version -a'
OS Name, Version, Hardware platform
Compiler Details (name, version)
- Application Details (name, version)
- Problem Description (steps that will reproduce the problem, if known)
- Stack Traceback (if the application dumps core)
Email the report to:
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In order to avoid spam, this is a moderated mailing list, and it might
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Please do NOT use this for general assistance or support queries.
Just because something doesn't work the way you expect does not mean it
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You can also make GitHub pull requests. If you do this, please also send
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----------------------------
See CONTRIBUTING
LEGALITIES
----------
A number of nations, in particular the U.S., restrict the use or export
of cryptography. If you are potentially subject to such restrictions
you should seek competent professional legal advice before attempting to
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