iSEC, EFF, and SonyBMG issued a joint press release yesterday, announcing yet another serious security bug in the SunnComm MediaMax copy protection software that ships on many SonyBMG compact discs. (SonyBMG has recalled CDs that use another copy protection system, XCP, but they have not yet recalled discs containing MediaMax.) As we've written before, the first time you insert a MediaMax-bearing CD into your Windows computer (assuming you have Windows autorun enabled, as most people do), MediaMax installs some software on your computer. Once this initial software is on your computer, you are vulnerable to the new attack. The gist of the problem is that MediaMax installs itself in a directory that anyone is allowed to modify, even users who otherwise run with heavily restricted security permissions. Any program that comes along can modify your MediaMax files, booby-trapping the files by inserting hostile software that will be run automatically the next time you insert a MediaMax-bearing CD into your computer. And because MediaMax is run with full administrator privileges, the hostile program gets to run with full privileges, allowing it to inflict any mischief it likes on your PC. Alex Halderman has discovered that the problem is worse than the press release indicates: You are vulnerable even if you decline the MediaMax license agreement. Simply inserting a MediaMax-bearing CD into your PC paves the way for an attacker to come along and set a booby-trap. The trap will be sprung the next time you insert such a disc. SonyBMG has released a patch that purports to fix the problem. However, our tests show that the patch is insecure. It turns out that there is a way an adversary can booby-trap the MediaMax files so that hostile software is run automatically when you install and run the MediaMax patch. The previously released MediaMax uninstaller is also insecure in the same way, allowing an adversary to booby-trap files so that hostile software is run automatically when you try to use the uninstaller. (These attacks are similar to the exploit described in iSEC's report, but they involve a different modification to the MediaMax files.) Because of these problems, we recommend for now that if you have a Windows PC, you (1) do not use the MediaMax patch, (2) do not use the previously released MediaMax uninstaller, and (3) do not insert a MediaMax-bearing CD into your PC. We have notified SonyBMG and MediaMax about these problems. We assume they will develop a new uninstaller that safely rids users' computers of the MediaMax software once and for all. The consequences of this problem are just as bad as those of the XCP rootkit whose discovery by Mark Russinovich started SonyBMG's woes. This problem, like the rootkit, allows any program on the system to launch a serious security attack that would normally be available only to fully trusted programs. According to the press release, SonyBMG intends to use MediaMax's banner ad display feature to warn users about these vulnerabilities. While this is a positive step, it will fail to reach users who have rejected the MediaMax license agreement. This group is at particularly high risk, since they are probably unaware that the software is installed on their computers. Worst of all, it is impossible to patch the millions of MediaMax-bearing CDs that are already out there. Every disc sitting on somebody's shelf, or in a record-store bin, is just waiting to install the vulnerable software on the next PC it is inserted into. The only sure way to address this risk is take the discs out of circulation. The time has come for SonyBMG to recall all MediaMax CDs. UPDATE (Dec. 9): Sony and MediaMax have issued a new patch. According to our limited testing, this patch does not suffer from the security problem described above. They have also issued a new uninstaller, which we are still testing. We'll update this entry again when we have more results on the uninstaller.