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Date: Sat, 20 Jan 2007 10:35:10 -0800
From: Carson Gaspar <carson@...tos.org>
To: bugtraq@...urityfocus.com
Subject: Re: Multiple OS kernel  insecure handling of stdio file descriptor

Peter Jeremy wrote:
> On 2007-Jan-18 22:21:52 +0800, XFOCUS Security Team <security@...cus.org> wrote:
>> The affected OSes allows local users to write to or read from restricted
>> files by closing the file descriptors 0 (standard input), 1 (standard
>> output), or 2 (standard error), which may then be reused by a called
>> setuid process that intended to perform I/O on normal files. the attack
>> which exploit this vulnerability possibly get root right.
> 
> This vulnerability has been known for years.  OpenBSD implemented a
> kernel check to block this attack in 1998.  FreeBSD and NetBSD have
> similar kernel checks and I believe glibc also has checks to block
> this.  It is disturbing that none of the commercial OS vendors appear
> to have bothered to protect against this.

Of course the _real_ problem is the badly written setuid app. Kernel 
checks for "special" fds are just a condom to try and protect against 
broken code. Not that such checks aren't a good idea (since so much code 
is so very broken), but any app that is vulnerable to this attack needs 
to be patched.

You'll note that the original advisory fails to specify any setuid apps 
that are vulnerable to this attack, other than their broken POC. *yawn*

-- 
Carson

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