Re: iDEFENSE Security Advisory: Linuxconf locally exploitable buffer overflow

[Dave Aitel <dave () immunitysec com>]

Hmm. A default run of sharefuzz finds this bug, which I then told
Mandrake about (as they are one of the few distributions that actually
does distribute it +s) back in January or so. Course, they never fixed
it, which goes to show you that sometimes the Open Source method is NOT
the best method. :>

So in this case, "Exclusively" means "Exclusive to iDefense and everyone
else in the whole world who bothers to do basic QA (run sharefuzz) on
their systems."

Dave Aitel
Immunity, Inc.



On Wed, 2002-08-28 at 11:58, David Endler wrote:
>  
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> iDEFENSE Security Advisory 08.28.2002
> Linuxconf locally exploitable buffer overflow vulnerability
>
> DESCRIPTION 
>
> A vulnerability exists in linuxconf which if the 
> LINUXCONF_LANG environment variable processes at least 964 
> bytes of data, a buffer overflow occurs, thereby allowing an 
> attacker to modify the return address of the function and 
> execute arbitrary code with root permissions.  iDEFENSE has an 
> exploit that allows a local user to launch a root shell on Red 
> Hat Linux 7.3 by targeting the latest version of linuxconf 
> 1.28r3. 
>
>
> ANALYSIS
>
> According to the author of Linuxconf, Jacques Gelinas 
> jack () solucorp qc ca, "linuxconf picks the variable and uses it 
> to format a path using snprintf. This works fine. In fact, the 
> receiving buffer is PATH_MAX large so even a 1000 characters 
> variable won't overflow it and even if this was the case, 
> snprintf would do its work. 
>
> Once the path is formatted, the corresponding file is opened. 
> If the file do not exist, an error message is formatted in a 
> string. This was the problem and sprintf was used instead of 
> snprintf there.
>
> There are two fixes. One is to use snprintf to format error 
> message at this place and the other is to look for appropriate 
> length for this variable (max 5 characters) immediately when it 
> is found."
>
>
> DETECTION
>
> This vulnerability affects any version of linuxconf 
> (essentially 6 years worth of distributions) that is installed 
> setuid root.  Generally, the four ways in which this utility 
> can be installed setuid are:
>
> 1.) Shipped by vendor (Red Hat does not ship linuxconf 
> setuid, but Mandrake does as do other linux vendors)
> 2.) Installed by RPM from the main site 
> (http://www.solucorp.qc.ca/linuxconf/) for each particular 
> linux OS (installs setuid root by default)
> 3.) Installed by source code also from main site 
> (http://www.solucorp.qc.ca/linuxconf/) but prompts for whether 
> to install setuid root 
> 4.) Installed in ways 1, 2, or 3 and manually set to setuid 
> root by the user for added functionality.
>
>
> WORKAROUND
>
> Remove the setuid bit from the linuxconf binary:
>
> $ chmod u-s /bin/linuxconf
>
>
> VENDOR RESPONSE
>
> iDEFENSE immediately contacted Jacques Gelinas and he provided 
> a source code patch.  iDEFENSE verified that the vulnerability 
> is mitigated in the newer distribution (1.28r4) of linuxconf.  
>
> An updated version (1.28r4) of linuxconf which addresses this 
> vulnerability will be available on August 28, 2002 at
> http://www.solucorp.qc.ca/linuxconf/ .
>
> Affected Linux vendors will make updates available 
> August 28th, 2002.
>
>
> DISCLOSURE TIMELINE
>
>
> August 9, 2002 - Exclusively disclosed to iDEFENSE
> August 19, 2002 - Disclosed to Vendor
> August 19, 2002 - Disclosed to iDEFENSE clients
> August 21, 2002 - Announcement to vendor-sec () lst de
> August 28, 2002 - Coordinated public disclosure by Linux vendors,  
>       Linuxconf maintainer, and iDEFENSE
>
>
> CREDIT
>
> This issue was exclusively disclosed to iDEFENSE by Euan Briggs
> (euan_briggs () btinternet com)
>
>
> http://www.idefense.com/contributor.html
>
>
> - - -dave
>
>
> David Endler, CISSP
> Director, Technical Intelligence
> iDEFENSE, Inc.
> 14151 Newbrook Drive
> Suite 100
> Chantilly, VA 20151
> voice: 703-344-2632
> fax: 703-961-1071
>
> dendler () idefense com
> www.idefense.com
>
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