Tor is an implementation of second generation Onion Routing, a connection-oriented anonymizing communication service.
Tor does not handle data correctly when specifically crafted data is sent, and also fails to properly verify a descriptor provided by a hidden service directory.
A remote attacker could cause a Denial of Service condition in both a Tor client or a Tor server.
There is no known workaround at this time.
All Tor users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=net-misc/tor-0.2.6.7"