CVE-2011-3389: _ssl module always disables the CBC IV attack countermeasure

[pitrou]

BPO	13885
Nosy	@loewis, @warsaw, @jcea, @pitrou, @benjaminp
Files	CVE-2011-3389-2.7.patch CVE-2011-3389-3.2.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2012-01-27.08:58:46.024>
created_at = <Date 2012-01-27.08:25:53.311>
labels = ['type-security', 'extension-modules']
title = 'CVE-2011-3389: _ssl module always disables the CBC IV attack countermeasure'
updated_at = <Date 2012-03-13.12:25:51.778>
user = 'https://github.com/pitrou'

bugs.python.org fields:

activity = <Date 2012-03-13.12:25:51.778>
actor = 'thoger'
assignee = 'none'
closed = True
closed_date = <Date 2012-01-27.08:58:46.024>
closer = 'pitrou'
components = ['Extension Modules']
creation = <Date 2012-01-27.08:25:53.311>
creator = 'pitrou'
dependencies = []
files = ['24335', '24336']
hgrepos = []
issue_num = 13885
keywords = ['patch']
message_count = 7.0
messages = ['152068', '152069', '152071', '152072', '152073', '152093', '155599']
nosy_count = 7.0
nosy_names = ['loewis', 'barry', 'jcea', 'pitrou', 'benjamin.peterson', 'thoger', 'python-dev']
pr_nums = []
priority = 'critical'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'security'
url = 'https://bugs.python.org/issue13885'
versions = ['Python 2.6', 'Python 3.1', 'Python 2.7', 'Python 3.2', 'Python 3.3']

[pitrou]

Original e-mail from Apple security team:

Follow-up: 187806281

SSL 3.0 and TLS 1.0 are vulnerable to an attack described at

http://www.openssl.org/~bodo/tls-cbc.txt

OpenSSL includes a countermeasure which prevents the attack, but python
2.7 has, around line 372 of Modules/_ssl.c:

SSL_CTX_set_options(self->ctx, SSL_OP_ALL);

SSL_OP_ALL includes SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS which disables the
countermeasure.

2.6 is similar.

[pitrou]

Attaching patches.

[python-dev]

New changeset 9a4131ada792 by Antoine Pitrou in branch '2.6':
Issue bpo-13885: CVE-2011-3389: the _ssl module would always disable the CBC IV attack countermeasure.
http://hg.python.org/cpython/rev/9a4131ada792

New changeset 8dec547c23d3 by Antoine Pitrou in branch '2.7':
Issue bpo-13885: CVE-2011-3389: the _ssl module would always disable the CBC IV attack countermeasure.
http://hg.python.org/cpython/rev/8dec547c23d3

[python-dev]

New changeset e7706bdaaa0d by Antoine Pitrou in branch '3.1':
Issue bpo-13885: CVE-2011-3389: the _ssl module would always disable the CBC IV attack countermeasure.
http://hg.python.org/cpython/rev/e7706bdaaa0d

New changeset 4386686a035d by Antoine Pitrou in branch '3.2':
Issue bpo-13885: CVE-2011-3389: the _ssl module would always disable the CBC IV attack countermeasure.
http://hg.python.org/cpython/rev/4386686a035d

New changeset d1390175fdc6 by Antoine Pitrou in branch 'default':
Issue bpo-13885: CVE-2011-3389: the _ssl module would always disable the CBC IV attack countermeasure.
http://hg.python.org/cpython/rev/d1390175fdc6

[pitrou]

This hopefully fixes the issue.

[benjaminp]

Thank you for handling this, Antoine!

[thoger]

Is the final patch going to enable empty fragments unconditionally and will ofter no way to disable them?

curl did that recently and ended up adding option to allow users to disable empty fragments when they break compatibility:

http://curl.haxx.se/docs/adv_20120124B.html
http://thread.gmane.org/gmane.comp.web.curl.library/34659
http://curl.haxx.se/libcurl/c/curl_easy_setopt.html#CURLOPTSSLOPTIONS
http://curl.haxx.se/docs/manpage.html#--ssl-allow-beast