Tor before 0.1.1.20 allows remote attackers to identify hidden services via a malicious Tor server that attempts a large number of accesses of the hidden service, which eventually causes a circuit to be built through the malicious server.
archives.seul.org/or/announce/Jan-2006/msg00001.html
secunia.com/advisories/18576
secunia.com/advisories/20514
security.gentoo.org/glsa/glsa-200606-04.xml
tor.eff.org/cvs/tor/ChangeLog
www.osvdb.org/22689
www.securityfocus.com/bid/18323
www.securityfocus.com/bid/19795
exchange.xforce.ibmcloud.com/vulnerabilities/24285