Difference between revisions of "T1 Font Integer Overflow"

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m (Ndrv setspec() Integer Overflow moved to DejaVu: A misunderstanding occurred.)
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The Ndrv setspec() Integer Overflow also known as DejaVu [http://twitter.com/#!/comex/status/88208990789578752] is a vulnerability used [[Saffron]].
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The '''T1 Font Integer Overflow''' (a.k.a '''DejaVu''' as it is very similar to the [[Malformed CFF Vulnerability]][https://twitter.com/comex/status/88208990789578752]) is an exploit used in [[Saffron]].
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== Credit ==
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* [[User:comex|comex]]
   
 
== Description ==
 
== Description ==
The pdf bug used in [[Saffron]] is like an integer checking problem. When dealing with op_callothersubr, arg_cnt is defined as an integer. arg_cnt is read from decoder->stack, which could be set to 0xfea50000 by charstring "fb ef". And this will bypass stack checking. Then "top -= arg_cnt" will make top points to data outside of decoder->stack. Actually it points to decoder->parse_callback.
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When dealing with op_callothersubr, arg_cnt is defined as an integer. arg_cnt is read from decoder&#8209;>stack, which could be set to <code>0xfea50000</code> by charstring "fb ef". And this will bypass stack checking. Then "top&nbsp;&#8209;=&nbsp;arg_cnt" will make top point to data outside of decoder&#8209;>stack. Actually it points to decoder&#8209;>parse_callback. decoder&#8209;>parse_callback address minus default address of that function to get ASLR offset. That's how it bypasses ASLR.
   
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This vulnerability was actually addressed by Apple in [[wikipedia:Mac OS X Snow Leopard|OS X v10.6.8]] ([http://support.apple.com/kb/HT4723 Security Update 2011-004]), but a fix was never pushed to [[iOS]]. (CVE-2011-0202).
Sources:
 
[http://twitter.com/#!/windknown/status/88170553948651520 1]
 
[http://twitter.com/#!/windknown/status/88171950886760448 2]
 
[http://twitter.com/#!/windknown/status/88172830029651968 3]
 
   
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When Apple released iOS 4.2.9/4.3.4 to patch this vulnerability, it received a different CVE identifier (CVE-2011-0226).
== Credit ==
 
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[[User:comex|comex]]
 
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== External Links ==
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* Tweets from <span class="plainlinks">@[https://twitter.com/windknown windknown]: [https://twitter.com/windknown/status/88170553948651520 1] [https://twitter.com/windknown/status/88171950886760448 2] [https://twitter.com/windknown/status/88172830029651968 3] [https://twitter.com/windknown/status/88173940391940096 4]</span>
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* [http://support.apple.com/kb/HT4723 KB HT4723]
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* [http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-0202 CVE-2011-0202]
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* [http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-0226 CVE-2011-0226]
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* [http://intrepidusgroup.com/insight/2011/07/reversing-jailbreakme-com-4/ Analasis by Intrepid US Group]
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* [http://esec-lab.sogeti.com/post/Analysis-of-the-jailbreakme-v3-font-exploit Analasis by Sogeti ESEC Labs]
   
 
[[Category:Exploits]]
 
[[Category:Exploits]]

Latest revision as of 00:12, 10 October 2012

The T1 Font Integer Overflow (a.k.a DejaVu as it is very similar to the Malformed CFF Vulnerability[1]) is an exploit used in Saffron.

Credit

Description

When dealing with op_callothersubr, arg_cnt is defined as an integer. arg_cnt is read from decoder‑>stack, which could be set to 0xfea50000 by charstring "fb ef". And this will bypass stack checking. Then "top ‑= arg_cnt" will make top point to data outside of decoder‑>stack. Actually it points to decoder‑>parse_callback. decoder‑>parse_callback address minus default address of that function to get ASLR offset. That's how it bypasses ASLR.

This vulnerability was actually addressed by Apple in OS X v10.6.8 (Security Update 2011-004), but a fix was never pushed to iOS. (CVE-2011-0202).

When Apple released iOS 4.2.9/4.3.4 to patch this vulnerability, it received a different CVE identifier (CVE-2011-0226).

External Links