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Re: CVE-2013-4287 Algorithmic complexity vulnerability in RubyGems 2.0.7 and older
From: Kurt Seifried <kseifried () redhat com>
Date: Wed, 18 Sep 2013 14:47:18 -0600

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On 09/17/2013 06:11 PM, Eric Hodel wrote:
On Sep 16, 2013, at 18:28, Kurt Seifried <kseifried () redhat com>
wrote:
On 09/14/2013 03:11 PM, Alexander Cherepanov wrote:
On 2013-09-10 09:32, Eric Hodel wrote:
The vulnerability can be fixed by changing the first grouping
to an atomic grouping in Gem::Version::VERSION_PATTERN in 
lib/rubygems/version.rb.  For RubyGems 2.0.x:

-  VERSION_PATTERN = 
'[0-9]+(\.[0-9a-zA-Z]+)*(-[0-9A-Za-z-]+(\.[0-9A-Za-z-]+)*)?'
# :nodoc: +  VERSION_PATTERN = 
'[0-9]+(?>\.[0-9a-zA-Z]+)*(-[0-9A-Za-z-]+(\.[0-9A-Za-z-]+)*)?'
# :nodoc:

For RubyGems 1.8.x:

-  VERSION_PATTERN = '[0-9]+(\.[0-9a-zA-Z]+)*' # :nodoc: + 
VERSION_PATTERN = '[0-9]+(?>\.[0-9a-zA-Z]+)*' # :nodoc:

This is not enough. The following script:

# Regexes are from 
https://github.com/rubygems/rubygems/blob/master/lib/rubygems/version.rb#L150




VERSION_PATTERN =
'[0-9]+(?>\.[0-9a-zA-Z]+)*(-[0-9A-Za-z-]+(\.[0-9A-Za-z-]+)*)?'
# :nodoc: ANCHORED_VERSION_PATTERN = 
/\A\s*(#{VERSION_PATTERN})*\s*\z/ # :nodoc: 
'1111111111111111111111111111.' =~ ANCHORED_VERSION_PATTERN

takes ~1m on my machine. The problem is not in VERSION_PATTERN
but in its possible repetition inside
ANCHORED_VERSION_PATTERN.


Great, I guess we're going to need a new CVE. Before I assign one
can we make sure we fix this so more fiddly expressions don't
cause problems? Thanks.

Here's a new patch to go with the new (unassigned) CVE.  This new
patch replaces regular expression matches that are susceptible to
backtracking with a parser-like approach.





This patch applies to RubyGems 2.1.x releases.  I will create
patches for RubyGems 1.8.23.1, 1.8.26, 2.0.9 and 2.1.4 if it there
is no obvious flaw seen in it.

I would like to release this fix by Monday, 23 September as I will
be traveling mid-week.

The vulnerable regular expression constants are still present, but
I can't think of a way to construct them that does not allow
backtracking.  I think they should be removed for the security fix
release, but a fellow maintainer is worried about backwards
compatibility and thinks they should be removed in the next feature
release (2.2).  What do people typically do?

Here is a script to check the patch:


Ok please please use CVE-2013-4363 for this issue (incomplete fix for
CVE-2013-4287).

- -- 
Kurt Seifried Red Hat Security Response Team (SRT)
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