Adobe Flash - ActionIf Integer Denial of Service

Adobe Flash Integer Overflow 

Author: Matthew Bergin

Date: June 15, 2010

Versions Affected: Flash10e.ocx v10.0.45.2

		   Flash10c.ocx v10.0.32.18 r32

Root Cause: ActionScript, "ActionIf"

Affect: Denial-of-Service, possible Command Execution

CVE: CVE-2010-3639

Desc: When Parsing an ActionIf ActionScript statement four args are passed

      to the function, an integer named i , a ubyte named ActionCode, a ushort

      named Length, and a short named BranchOffset. If the BranchOffset is -305 or 

      smaller it will cause an Access Violation when reading data from a 

      invalid memory address. The last 16-bits of the address are controlable

      with the size of the BranchOffset argument. Any data which is in a valid

      segment of memory near the controlled address can be read causing Memory

      Disclosure. This would be used well in combination with a memory corruption

      vulnerability in order to bypass ASLR. 



      In doing my initial research I found a lot of interesting things along the way.

      Flash10c is not vulnerable in the same way Flash10e is. I initially discovered

      the integer overflow in Flash10c while fuzzing SWF. I didnt fuzz it via a web

      browser but instead used a free application which uses the modules in a more

      direct manner. Flash10c is not able to be attacked via a browser as far as I

      have been able to tell. However, I have found during my research that Flash10e

      is loaded as a module when any Flash object is encountered. I am unsure as to

      if this is a configuration issue or not. In addition to this, while debugging

      this issue I found that both versions have a self-changing CRC which inhibits

      keeping break points set.



      Another interesting note is that when confirming the PoC on Flash Movie Player

      i noticed that if you open the file with the File -> Open drop down menu, the

      PoC will not hit the vulnerable code causing a crash. However, if you register

      the swf extension to Flash Movie Player and "double-click" the PoC file to run

      it, Flash Movie Player will hit the vulnerable code every time. 



      The PoC code would be best embedded into HTML for remote attacks but can be

      attacked in any manner in which Flash10c.ocx/Flash10e.ocx are loaded as modules

      into memory.





Fuzzed Application: EolSoft Flash Movie Player (downloads.cnet.com) v1.5



Crash Details:



Access Violation

Exception caught at 1009cb23 mov al,[eax+ecx]

EAX:0267010c EBX:00e990b4 ECX:fffffef3 EDX:00e9b038

ESI:00e80000 EDI:00e990b0 ESP:0012f780 EBP:0012f99c



Reversing:



struct SWFTAG Tag[7], value DoAction

struct ACTIONRECORD ActionTag[6], value ActionIf, starts @ E3h size 5h

int i, value 0

ubyte ActionCode, value 157

ushort Length, value 2

short BranchOffset, value -305



BranchOffset is located @ E6h-E7h



PoC: https://github.com/offensive-security/exploit-database-bin-sploits/raw/master/sploits/15426.rar (adobe_flash_int_ovrflw_poc.rar)