Macromedia Flash Activex Buffer overflow Release Date: 05/02/2002 Severity: High (Remote code execution) Systems Affected: Flash Activex Ocx Version 6, revision 23 (Possibly older versions) Forward: This is an unusual advisory in a number of ways. One, it was found while investigating an access error encountered during normal web surfing, which was suspicious. Within a few hours we had confirmed on multiple Operating Systems that this was an exploitable condition that overwrote EIP. Two, while we tested on these systems with the latest install from the vendor's site, when we contacted the vendor they informed us that they had just released a new build this same day which already fixed the problem. They asked us to confirm this. We tried the link they gave us and it did indeed fix the problem and was a new build. Testing the link later that night confirmed the link we used to install the ocx now had the fixed, latest version. In this, we congratulate Macromedia for: finding the bug, fixing it, and releasing the build in a timely fashion. This truly shows that they are dedicated to security just as they have stated they are. However, because there is a signed flash ocx out there which has been downloaded by an untold number of people, and potentially could still be used in an exploit scenario against those without the latest ocx we felt the need to release this advisory. Furthermore, this issue was found in the wild, and it is not safe to assume it could not be found by others with malicious intent. Nor do we believe it is safe to assume this has not been found by users with malicious intent. There are further issues with old activex objects which have such vulnerabilities which will be discussed in the description section. Description: A vulnerability in the parameter handling to the Flash OCX, which could lead to the execution of attacker supplied code via email, web or any other avenue in which Internet Explorer is used to display html that an attacker can supply. This includes software which uses the web browser activex. All users of Internet Explorer are potentially affected because this is a Macromedia signed ocx. We advise them to upgrade their flash version immediately to version 6, revision 29. Example: Where X overwrites the EIP consistently across Windows platforms. Technical Description: Flash.ocx is an activex object installed with Internet Explorer, and is used to display flash objects on the web. Proper bounds checking is not in place in the "movie" parameter which overwrites EIP at an unsaid, but fixed number of bytes across Windows platforms. Because the ocx is signed by Macromedia: there is a chance the older activex could be used against people without flash; people whom have an older version of flash not affected may be forced to "upgrade" to the affected version; and, of course, those with the affected versions need to upgrade lest the exploit works out of the box on them. There has been considerable debate about legacy activex objects which have exploits within them. In general, if someone uses the codebase parameter to point to an affected version of the activex, the system will first try and grab the activex from Microsoft's activex store on the web. Then, it will try the activex specified in the codebase tag by the malicious user. We do not believe this method is full proof. We do not believe the method is full proof because of the potential of the activex storehouse check failing and because of the potentiality for the activex to be called by other methods. (At least a few potential other methods are in the RFC for applets and objects). However, the other option of setting the "kill bit" for the affected activex and reassigning the fixed activex version with a new classid is only a suggestion we will make in this case. We do not believe it is necessarily mandatory. Risk should be mitigated to a satisfactory level by users upgrading to the new ocx. Vendor Status: Visit Macromedia's site to get the latest Flash ocx to eliminate these issues. http://www.macromedia.com/shockwave/download/index.cgi?P1_Prod_Version=Shock waveFlash Credit: Drew Copley Greetings: Fat code: presented by Yahoo and Weight Watchers. KROQ, and corn dog manufacturers world wide. Copyright (c) 1998-2002 eEye Digital Security Permission is hereby granted for the redistribution of this alert electronically. It is not to be edited in any way without express consent of eEye. 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