Difference between revisions of "T1 Font Integer Overflow"

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(apple patched this)
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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. decoder‑>parse_callback address minus default address of that function to get ASLR offset. That's how it bypasses ASLR.
 
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 {{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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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] (Its CVE identifier is ''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).
 
When Apple released iOS 4.2.9/4.3.4 to patch this vulnerability, it received a different CVE identifier (CVE-2011-0226).

Revision as of 14:58, 21 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 bypasses ASLR.

This vulnerability was actually addressed by Apple in Template:Wp/Security Update 2011-004 (Its CVE identifier is 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).

Sources