[tor-bugs] #4587 [Tor Client]: Bugs in tor_tls_got_client_hello()

Tor Bug Tracker & Wiki torproject-admin at torproject.org
Mon Dec 5 01:56:21 UTC 2011

#4587: Bugs in tor_tls_got_client_hello()
 Reporter:  Sebastian      |          Owner:  nickm             
     Type:  defect         |         Status:  assigned          
 Priority:  major          |      Milestone:  Tor: 0.2.3.x-final
Component:  Tor Client     |        Version:                    
 Keywords:  tls handshake  |         Parent:                    
   Points:                 |   Actualpoints:                    

Comment(by asn):

 I forgot to mention that if you send a ClientHello when the server expects
 a Certificate (`SSL3_ST_SR_CERT_A` or `SSL3_ST_SR_CERT_B`), the server
 will go back to SSL3_ST_SR_CLNT_HELLO_C, restart the handshake, send a
 ServerHello, a Certificate and a ServerKeyExchange. So you don't need to
 issue a renegotiation to load the server through a single TCP connection.

 This means that if we are serious about SSL DoS vectors, we must discard
 any clients doing the above. Furthermore, implementing this, immediately
 introduces a bridge fingerprint, which this time cannot simply be removed
 by disabling renegotiation/v2.

 (You can PoC this using my clienthellotest.py)

Ticket URL: <https://trac.torproject.org/projects/tor/ticket/4587#comment:22>
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