Bugtraq: Symlink vulnerabilities in mailmgr

[Marco van Berkum <m.v.berkum () obit nl>]

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Title          : Symlink vulnerabilities in mailmgr
Bug finder     : Marco van Berkum (m.v.berkum () obit nl)
Website        : http://ws.obit.nl
URL to mailmgr : http://web.onda.com.br/orso/mailmgr.html
Tested version : Mailmgr-1.2.3
Date           : 12 Feb 2004
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About mailmgr
-------------
Mailmgr is a Sendmail Analysis Report Generator that can be used to 
create HTML reports.
Severity
--------
High when mailmgr is executed as root, root owned files can then be 
overwritten.
Problem description
-------------------
By default mailmgr uses predictable temporary filenames placed in /tmp, 
which allows local users to launch a  symlinkattack to overwrite files 
owned by users or superusers that run mailmgr to generate mailreports. 

By default these are the temporary filenames:

/tmp/mailmgr.unsort
/tmp/mailmgr.tmp
/tmp/mailmgr.sort

Exploit
-------
Simply create a symlink in /tmp to any file you wish to overwrite, for 
example: 

/tmp/mailmgr.unsort -> /file/you/whish/to/corrupt

When the user (could be root) executes mailmgr the targetfile will be 
corrupted.
Solution
--------
Use the temporary_dir directive in /usr/local/etc/mailmgr.conf to point 
to a directory that does not have a sticky bit set.