Tor before 0.2.4.23 and 0.2.5 before 0.2.5.6-alpha maintains a circuit after an inbound RELAY_EARLY cell is received by a client, which makes it easier for remote attackers to conduct traffic-confirmation attacks by using the pattern of RELAY and RELAY_EARLY cells as a means of communicating information about hidden service names.
CVSS Severity (version 2.0):
Impact Subscore: 4.9
Exploitability Subscore: 8.6
CVSS Version 2 Metrics:
Access Vector: Network exploitable
Access Complexity: Medium
Authentication: Not required to exploit
Impact Type: Allows unauthorized disclosure of information; Allows unauthorized modification
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[tor-talk] 20140730 Tor 0.2.5.6-alpha is out
[tor-announce] 20140730 Tor 0.2.4.23 is released
[tor-announce] 20140730 Tor security advisory: "relay early" traffic confirmation attack