Project

General

Profile

Actions

Bug #5353

closed

TLS v1.0 and less - Attack on CBC mode

Added by MartinBosslet (Martin Bosslet) about 13 years ago. Updated almost 12 years ago.

Status:
Closed
Target version:
ruby -v:
-
Backport:
[ruby-core:39673]

Description

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.)

Actions

Also available in: Atom PDF

Like0
Like0Like0Like0Like0Like0Like0Like0Like0Like0Like0Like0Like0Like0