[issue20994] Disable TLS Compression

[Christian Heimes]

Christian Heimes added the comment:

Issue #28043 did disable compression along with other improvements. 3.5 is now 
out of scope but I'm considering to backport #28043 to 2.7. I'm closing this 
issue in favor of #28043.

--
resolution:  -> duplicate
stage: needs patch -> resolved
status: open -> closed
superseder:  -> Sane defaults for SSLContext options and ciphers

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[issue20994] Disable TLS Compression

[Christian Heimes]

Christian Heimes added the comment:

For 3.6 and 3.7, _ssl__SSLContext_impl() now sets NO_COMPRESSION.

--
assignee:  -> christian.heimes
components: +SSL
versions:  -Python 3.6, Python 3.7

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[issue20994] Disable TLS Compression

[Christian Heimes]

Christian Heimes added the comment:

the default context sets context.options |= getattr(_ssl, "OP_NO_COMPRESSION", 
0), _create_unverified_context() is missing that line.

--
stage:  -> needs patch
type:  -> security
versions: +Python 3.6, Python 3.7 -Python 3.3, Python 3.4

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[issue20994] Disable TLS Compression

[Christian Heimes]

Changes by Christian Heimes :


--
priority: normal -> high

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[issue20994] Disable TLS Compression

[Georg Brandl]

Georg Brandl added the comment:

I wouldn't consider this important enough for 3.2; since it lacks the means to 
do the opt-back-in.

--
nosy: +georg.brandl
versions:  -Python 3.2

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[issue20994] Disable TLS Compression

[Alex Gaynor]

Alex Gaynor added the comment:

Pinging on this, since the SSL backport landed, concerns about an inability to 
change this behavior on python2 are no longer there. At a minimum I think we 
should include this flag in the default and stdlib contexts.

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[issue20994] Disable TLS Compression

[Antoine Pitrou]

Antoine Pitrou added the comment:

Now that the backport has landed, I think you're welcome to do any further 
necessary tweaks.

By the way, as mentioned in the comments, I think we could add 
SSL_OP_NO_COMPRESSION to ssl.OP_ALL in all versions.

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[issue20994] Disable TLS Compression

[Donald Stufft]

New submission from Donald Stufft:

Since Python 3.3 the ssl module has supported the ability to opt in to 
disabling TLS Compression [1]. However TLS Compression has the problem that it 
typically leaks data through an attack known as CRIME. CRIME is specific to 
HTTP but the type of attack it employs is not.

I believe that CPython should just flat out disable TLS Compression and it 
should do so in all currently active branches (2.7, 3.2+). The patch is fairly 
minor however there is the question of how that should be handled in 3.3+ where 
there would be a now useless flag and method on SSLContext. The likelhood for 
breakage is fairly low and all modern browsers have already permanently 
disabled it.

[1] http://bugs.python.org/issue13634

--
messages: 214234
nosy: christian.heimes, dstufft, ncoghlan, pitrou
priority: normal
severity: normal
status: open
title: Disable TLS Compression
versions: Python 2.7, Python 3.2, Python 3.3, Python 3.4, Python 3.5

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[issue20994] Disable TLS Compression

[Antoine Pitrou]

Antoine Pitrou added the comment:

It would probably be sufficient to add OP_NO_COMPRESSION to OP_ALL.

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[issue20994] Disable TLS Compression

[Donald Stufft]

Donald Stufft added the comment:

Ah, I hadn't noticed the OP_ALL thing, in 3.3+ adding OP_NO_COMPRESSION to 
OP_ALL would be reasonable. That would disable TLS Compression by default, 
still provide people the ability to disable TLS Compression if they don't use 
OP_ALL, and provide a way to enable it if they want it.

Do you think it'd be OK to just disable TLS Compression in 2.7 and 3.2 without 
the option to turn it back on? I think that would be fine personally.

--

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[issue20994] Disable TLS Compression

[Antoine Pitrou]

Antoine Pitrou added the comment:

 Do you think it'd be OK to just disable TLS Compression in 2.7 and 3.2
 without the option to turn it back on? I think that would be fine
 personally.

I'm not enough of a TLS expert, but it sounds ok.

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[issue20994] Disable TLS Compression

[Alex Gaynor]

Changes by Alex Gaynor alex.gay...@gmail.com:


--
nosy: +alex

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[issue20994] Disable TLS Compression

[Alex Stapleton]

Alex Stapleton added the comment:

CRIME is not universally applicable to all TLS connections and it requires some 
cooperation from the application to work. In fact for a Python TLS client it 
seems quite unlikely for an application to be vulnerable. The attack in the 
paper leverages an insecure website to inject JavaScript to issue crafted 
requests to a secure one. i.e. It requires both compression and some degree of 
remote code execution to work. Perhaps there are ways to extend the attack to 
apply to more common Python TLS client usage though?

Also some users will absolutely want to manually re-enable compression, please 
don't disable it entirely.

--
nosy: +Alex.Stapleton

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[issue20994] Disable TLS Compression

[Donald Stufft]

Donald Stufft added the comment:

To be specific it doesn't require any remote code execution to work, it just 
requires you to be able to influence the content of the responses that the 
client is receiving.

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[issue20994] Disable TLS Compression

[Donald Stufft]

Donald Stufft added the comment:

This is a simple patch, it simple disables TLS Compression by default. If a 
user wants to add it back they can create their own SSLContext and do


ctx = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
ctx.options = ~ssl.OP_NO_COMPRESSION

This should be able to apply against 3.2+ although it would only be 3.3+ that 
ssl.OP_NO_COMPRESSION is available to disable it, although a user could still 
hard code the constant in themselves.

This still leaves 2.7 out in the open here, what I'd like to do is just disable 
it and if someone really *needs* TLS Compression they can use pyopenssl to get 
that back. This is a reversal of the current situation where in order to get 
the safer value you have to use pyopenssl.

--
keywords: +patch
Added file: 
http://bugs.python.org/file34531/disable-ssl-compression-default.diff

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[issue20994] Disable TLS Compression

[Arfrever Frehtes Taifersar Arahesis]

Changes by Arfrever Frehtes Taifersar Arahesis arfrever@gmail.com:


--
nosy: +Arfrever

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[issue20994] Disable TLS Compression

[Donald Stufft]

Donald Stufft added the comment:

Here's the same patch for Python 2.7, it's basically the same thing just at a 
different location.

--
Added file: http://bugs.python.org/file34532/disable-ssl-compression-2.7.diff

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