New Flash XSS technique (thousands of websites at risk)
This week I spent a good amount of time studying the recent attack technique disclosed about XSS issues in common Shockwave Flash Files. At first I thought, “eh, looks cool, but probably just some theoretical edge case”. Then in working with white paper author Rich Cannings I came to understand that the details are more complex than I originally gave credit. Apparently the scope of the problem is easy to underestimate with potentially hundreds of thousands of websites at risk (right, as if we needed more XSS to deal with). The other thing is that reasonably workable fixes are going to be a long time coming.
In many ways the issue is similar to that of Adobe’s Universal XSS problem from last year. At its simplest, this issue describes that vulnerable Flash files can be used to XSS the hosting domain. The URL would look something like this:
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