From: Martin Bosslet <Martin.Bosslet@...> Date: 2012-02-23T20:42:52+09:00 Subject: [ruby-core:42835] [ruby-trunk - Bug #5353] TLS v1.0 and less - Attack on CBC mode Issue #5353 has been updated by Martin Bosslet. Hiroshi Nakamura wrote: > The original proposal from Martin, turning off the SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS bit by default, is still open. Yes, to follow up on this: it remains to decide how this should be handled in libraries that use OpenSSL::SSL, such as Net::HTTP. In Net::HTTP's case (and I could imagine probably in most of the other cases, too), the SSLContext object is not directly accessible, so we can't configure 0/n splitting there now. Two paths could be chosen to enable the functionality. Either patching each of the libraries by offering some way to configure 0/n splitting - or we could simply make 0/n splitting the default. The latter would only require one central change, but bears the potential to break existing installations. Generally we are in favor of staying as compatible as possible for 2.0, but it would also mean that things like the "BEAST" attack will remain feasible in the future. So should we make this the default in trunk? The time until 2.0 gets released should give incompatible setups enough time to patch their environment? ---------------------------------------- Bug #5353: TLS v1.0 and less - Attack on CBC mode https://bugs.ruby-lang.org/issues/5353 Author: Martin Bosslet Status: Open Priority: High Assignee: Category: ext Target version: 2.0.0 ruby -v: - A well-known vulnerability of TLS v1.0 and earlier has recently gained some attention: http://www.theregister.co.uk/2011/09/19/beast_exploits_paypal_ssl/ Although this has been known for a long time (http://www.openssl.org/~bodo/tls-cbc.txt), and a fix for this has been provided, in reality most applications seem to be working with SSL_OP_ALL which is a flag that enables some bug workarounds that were considered harmless. We, too, use this in ossl_sslctx_s_alloc(VALUE klass) in ossl_ssl.c. Unfortunately, this flag also includes SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS which disables the fix for the "CBC vulnerability". Here is what a comment says about the flag (OpenSSL 1.0.0d) /* Disable SSL 3.0/TLS 1.0 CBC vulnerability workaround that was added * in OpenSSL 0.9.6d. Usually (depending on the application protocol) * the workaround is not needed. Unfortunately some broken SSL/TLS * implementations cannot handle it at all, which is why we include * it in SSL_OP_ALL. */ If I understand http://www.openssl.org/~bodo/tls-cbc.txt correctly, the most notable implementation that does not play well with these empty fragments was (is?) IE - I don't know how this has evolved over time, I would have to research further. An easy fix for the situation would be to discard SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS, but this would risk affecting existing installations. What do you propose? Should we solve this before the 1.9.3 release? (PS: The actual attack and fix are outlined in http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.61.5887&rep=rep1&type=pdf The attack to be presented by Thai Duong and Juliano Rizzo at http://ekoparty.org/cronograma.php (caution: currently the site is victim to the "reddit effect") is very likely to be based on what was already known and should therefore hopefully require no further fixes.) -- http://bugs.ruby-lang.org/