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 ( 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


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: (adobe_flash_int_ovrflw_poc.rar)