[SECURITY] [DSA 2993-1] tor security update

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Debian Security Advisory DSA-2993-1                   security@debian.org
http://www.debian.org/security/                           Peter Palfrader
July 31, 2014                          http://www.debian.org/security/faq
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Package        : tor
CVE ID         : CVE-2014-5117

Several issues have been discovered in Tor, a connection-based
low-latency anonymous communication system, resulting in information
leaks.

o  Relay-early cells could be used by colluding relays on the network to
   tag user circuits and so deploy traffic confirmation attacks
   [CVE-2014-5117].  The updated version emits a warning and drops the
   circuit upon receiving inbound relay-early cells, preventing this
   specific kind of attack.  Please consult the following advisory for
   more details about this issue:

     https://blog.torproject.org/blog/tor-security-advisory-relay-early-traffic-confirmation-attack

o  A bug in the bounds-checking in the 32-bit curve25519-donna
   implementation could cause incorrect results on 32-bit
   implementations when certain malformed inputs were used along with a
   small class of private ntor keys.  This flaw does not currently
   appear to allow an attacker to learn private keys or impersonate a
   Tor server, but it could provide a means to distinguish 32-bit Tor
   implementations from 64-bit Tor implementations.


The following additional security-related improvements have been
implemented:

o  As a client, the new version will effectively stop using CREATE_FAST
   cells.  While this adds computational load on the network, this
   approach can improve security on connections where Tor's circuit
   handshake is stronger than the available TLS connection security
   levels.

o  Prepare clients to use fewer entry guards by honoring the consensus
   parameters.  The following article provides some background:

     https://blog.torproject.org/blog/improving-tors-anonymity-changing-guard-parameters

For the stable distribution (wheezy), these problems have been fixed in
version 0.2.4.23-1~deb7u1.

For the testing distribution (jessie) and the unstable distribution
(sid), these problems have been fixed in version 0.2.4.23-1.

For the experimental distribution, these problems have been fixed in
version 0.2.5.6-alpha-1.

We recommend that you upgrade your tor packages.

Further information about Debian Security Advisories, how to apply
these updates to your system and frequently asked questions can be
found at: http://www.debian.org/security/