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I updated the whitepaper "TLS / SSLv3 vulnerability explained" :

Updated 18.11.2009 : Added SMTP over TLS attack scenario, added s_client testcase
Updated 30.11.2009 : Added FTPS analysis, new attacks against HTTPS (injecting responses and downgrading to HTTP)  

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In order to allow me to update in a more convenient manner, the latest updates will be added to the G-SEC blog only. Once the final revision of this blog post will be achieved I will update this blog with the latest one.

  • Updated 17:50 GMT+1 / 05.2009 - added Mitigation / Impact 
  • Updated 16:40 GMT+1 / 06.2009 - added IETF draft 
  • Updated 14:35 GMT+1 / 07.2009 - added SSLTLS Test Tool 
  • Updated 16:34 GMT+1 / 07.2009 - added OpenSSL patch 
  • Updated 13:00 GMT+1 / 09.2009 - added GNUTLS patch 
  • Updated 19:40 GMT+1 / 09.2009 - added testing TLS renegotiation support 
  • Updated 21:29 GMT+1 / 09.2009 - added Apache patch, Mozilla Bug ID, Redhat Bug ID, Mozilla patch disabling tls renegotiation, Tomcat mitigation 
  • Updated 21:00 GMT+1 / 12.2009 - added a whitepaper trying to explain the vulnerability and it's implications to a broader audience

After some in-house tests, we can confirm that the vulnerability presented at indeed real and should pose a significant threat to most. The vulnerability has been discovered by "Marsh Ray".

We are currently looking into possible mitigations and will update this blog post regularly with more information regarding said vulnerability - if available.


  • OpenSSL 0.9.81 ( Attention: OpenSSL removed the TLS/SSL renegotiation feature from this package - you need to test application before/after updating to this version ) (via ISC)
  • GnuTLS patch (implements a new TLS extension proposed in the IETF Draft) (via SID)
  • Apache patch (patches renogtiation prefix attacks at the application layer, still need openssl fixes for other attacks)
Impacts :
Currently known to exist
  • In general an attacker positioned in the middle of a connection may inject arbritary content into the beginning of an authenticated strea, it will be interesting to see what potential impact this vulnerability has within each of the applications / protocols supporting it. IMAPS, FTPSSL, POP3 etc
  • For web servers - Attackers (if in the middle) can inject data into a segment that is authenticated to the web server, the web server will merge those requests and process them. (GET requests are trivially exploitable, POST are not known to be)
Mitigations :
  • Monitor renegotiation requests
  • To mitigate possible attacks against web applications - use an IPS/IDS/Application firewall to catch recurrent HTTP request that are enclosed within each other