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Difference between revisions of "T1 Font Integer Overflow"
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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 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. |
+ | 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 bypass ASLR. |
This vulnerability was actually addressed by Apple in {{wp|Mac OS X Snow Leopard|Mac OS X v10.6.8}}/[http://support.apple.com/kb/HT4723 Security Update 2011-004], but a fix was never pushed to [[iOS]]. Its CVE identifier is ''CVE-2011-0202''. |
This vulnerability was actually addressed by Apple in {{wp|Mac OS X Snow Leopard|Mac OS X v10.6.8}}/[http://support.apple.com/kb/HT4723 Security Update 2011-004], but a fix was never pushed to [[iOS]]. Its CVE identifier is ''CVE-2011-0202''. |
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Revision as of 23:57, 11 July 2011
The T1 Font Integer Overflow (A.K.A DejaVu as it is very similar to the Malformed CFF Vulnerability[1]) is a vulnerability used in Saffron.
Credit for Exploitation
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 bypass ASLR.
This vulnerability was actually addressed by Apple in Template:Wp/Security Update 2011-004, but a fix was never pushed to iOS. Its CVE identifier is CVE-2011-0202.
