remote DoS in Mozilla 1.0

[Tom <tom () lemuria org>]

Author            
======
Tom Vogt <tom () lemuria org>
http://web.lemuria.org/


Affected
========
Mozilla 1.0 and earlier
verified on Linux and Solaris, other Unixes most likely affected as well.


Effect
======
System becomes unuseable or X windows crashes 
(varies depending on system configuration)


Description
===========
When loading pages with a specially prepared (or erroneous) stylesheet,
mozilla and X windows (not restricted to XFree) exhibit any of two 
undesireable behaviours. This seems to depend on the local system 
configuration, especially to the presence of xfs, but bug reports so far
are inconclusive.
In one scenario, X simply crashes, taking everything with it. This will result
in the loss of unsaved work.
In scenario two, memory useage of the X server explodes until the machine
reaches the thrashing point, at which point only a hard kill (-9) of the
X server can save it, provided there are enough system resources left to
issue the kill.

Some systems see no crash, but random misbehaviour of X components that often
require a shutdown of the X server to fix. See the follow ups in bugzilla
for a full description of these various behaviours.

The bug is triggered by a huge font setting done through CSS. Depending on
the end user's system configuration, this will either trigger an abort in
the XFree86 code ("Beziers this large not supported") or cause an
explosive use of memory. It is unknown how much memory could get consumed,
but follow-ups to the mozilla bug verify that machines with 1 GB of
memory still reach the thrashing point.


Example
=======
Include a huge font size in your style sheet definition, e.g.:
body { font-size: 1666666px; }

http://www.adeliesolutions.com/Projects/
http://bugzilla.mozilla.org/attachment.cgi?id=87009&action=view


Vendor Contact
==============
filed as mozilla bug #150339
http://bugzilla.mozilla.org/show_bug.cgi?id=150339
Mozilla team scrambled immediately

also filed with the XFree86 team, no reaction so far


Solution/Patches
================
No patches have been issued so far, though the mozilla team appears to be
at work and a patch should be available soon.

Another solution would be turning off stylesheets. Mozilla does not have an
option for doing so in the preferences dialog, so this must be done either
in the preferences file manually, or by editing the source code. I have not
reviewed this option further.
Unchecking the "allow documents to use other fonts" button in preferences
does NOT provide a workaround.


Author Statement
================
Aside from the fact that I don't believe in "responsible disclosure", this
is already public knowledge through bugzilla.
Kudos to the mozilla team for prompt and competent reactions.






-- 
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