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Difference between revisions of "T1 Font Integer Overflow"
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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]] |
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== Description == |
== Description == |
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| − | + | When dealing with op_callothersubr, arg_cnt is defined as an integer. arg_cnt is read from decoder‑>stack, which could be set to <code>0xfea50000</code> 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. |
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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). |
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| − | Sources: |
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| − | [http://twitter.com/#!/windknown/status/88170553948651520 1] |
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| − | [http://twitter.com/#!/windknown/status/88171950886760448 2] |
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| − | [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). |
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| − | == 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] |
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| + | |||
| + | [[Category:Exploits]] |
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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).
