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Symlink vulnerabilities in mailmgr



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Title          : Symlink vulnerabilities in mailmgr
Bug finder     : Marco van Berkum (m.v.berkum@xxxxxxx)
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
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Mailmgr is a Sendmail Analysis Report Generator that can be used to create HTML reports.

Severity
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High when mailmgr is executed as root, root owned files can then be overwritten.

Problem description
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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
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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
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Use the temporary_dir directive in /usr/local/etc/mailmgr.conf to point to a directory that does not have a sticky bit set.