5.8 - DSA-2993

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.