WMF vulnerability not an accident? Was it an intentional backdoor?
I’m not quite sure if I’m willing to attribute to design, what I could attribute to a mistake… but, slashdot has pointed out that Steve Gibson in his latest Security Now! podcast (link is to transcript), is suggesting that it appears as though the WMF vulnerability of recent weeks appears (to him) to have been INTENTIONALLY included as a means of a remote backdoor.
Basically, he was in process of designing a test for the vulnerability with hopes of fixing it for the versions of Windows that it is “not critical” for… what he found was very interesting. The setAbortProc, first has no business being involved with wmf rendering. So, from his transcript…
each record in a metafile begins with a four-byte length, followed by a two-byte function number. So in other words, each metafile record has six bytes minimum that it can possibly be in size. Oh, and since the size is in words, the smallest possible size for a metafile record would be three words long, or six bytes. Look, the reason I had problems making this exploit happen initially is I was setting the length correctly. It turns out that the only way to get Windows to misbehave in this bizarre fashion is to set the length to one, which is an impossible value. I tried setting it to zero. It didn’t trigger the exploit. I tried setting it to two, no effect. Three, no effect. Nothing, not even the correct length. Only one.
Like, I say, I’m not sure whether to chalk it up to a designed trigger for a backdoor, or just… “oh I never imagined someone would try setting it to one…” but, it wouldn’t be THAT shocking if it is a trigger for a backdoor. If you believe some, there are many other hidden backdoors in Windows. Given that Windows is closed source, well, we really can’t technically know about any backdoors can we?
Anyway, he’s researching the issue further and expects to have an update in next weeks podcast. At this point though, I suspect there is no way we could know for sure whether it was there intentionally or not, we can only guess. He did make the point that there have been other WMF vulnerabilities and they recently stopped EVERYTHING they were doing at Microsoft and went through a massive security audit of their code, which he suggests, given past experience should have included a thorough look at WMF related items. He suggests that this should have showed up in that review. It’ll be interesting to see what he has to say next week and what other folks have to say about this.