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ERA IT Solutions  AG            http://www.era-it.ch

Security Advisory  -   xfstt-1.4 vulnerability   -   11/07/2003
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1. Vulnerability description
2. Impact
3. Notification status
4. Exploit status
5. Contact

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1. Vulnerability description

The X Fontserver for Truetype fonts 1.4 
(http://developer.berlios.de/projects/xfstt/
<http://freshmeat.net/redir/xfstt/11925/url_homepage/xfstt>) contains 
vulnerability
holes which can be initiated remotely.

In xfstt.cc:working() the switch(buf[0]) { ..  } statement is very 
insecurely
implemented. No boundary checks on any network-received buffers are done.
At least in two cases, namely FS_QueryXExtents8 and FS_QueryXBitmaps8, 
it is possible
to arrange a packet which sets 'req->num_ranges' to a very big number 
that causes an
array out of boundary access within the next for-loop. This bug leads to 
a segmentation
fault of the specific child and might even let an attacker execute 
arbitrary code.


2. Impact

It's yet unclear if this bug is exploitable or not. With a specially crafted
packet you can disable/DoS the daemon.


3. Notification status

The Author of xfstt (Guillem Jover) has been notified on May 28, 2003. 
There is no
patch available, though version 1.5 is soon to be released.


4. Exploit status

A proof-of-concept DoS exploit exists, albeit unreleased.


5. Contact

era@era-it.ch

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Thanks to Jonathan Heusser who originally found this bug.