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Date: Fri, 3 Jun 2016 21:31:04 +0200
From: Sebastian Pipping <sebastian@...ping.org>
To: oss-security@...ts.openwall.com
Subject: Re: expat hash collision fix too predictable?

Hi!


On 05.04.2012 11:30, Marcus Meissner wrote:
> Hi,
> 
> while reviewing a expat regression (likely caused by the hash collision denial of service fix, but unclear)
> i stumbled about the randomness it uses.
> 
> 	static unsigned long
> 	generate_hash_secret_salt(void)
> 	{
> 	  unsigned int seed = time(NULL) % UINT_MAX;
> 	  srand(seed);
> 	  return rand();
> 	}
> 
> and it is seeded once at parser object creation.
> 
> This is better than not seeding, but I am not sure if it is sufficient.
> 
> Ciao, Marcus
> 

Please excuse bumping this thread.  It think it may need another CVE:

The call to srand(3) can reduce the security of the calling application,
depending on what it is doing with srand(3)/random(3).  This behavior is
recognized as a bug by Fedora, too
(https://bugzilla.redhat.com/show_bug.cgi?id=1197087).

There are multiple related commits in Expat's Git repository.  I am
happy to extract a single to-the-point patch for your version of Expat
and operating system platform from that for you, if needed.

Best



Sebastian

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