(a.k.a. MSRC 8769, MS09-054, CVE-2009-1547, “Data Stream Header Corruption Vulnerability”)
Microsoft fixed a bug in Internet Explorer’s “Content-Encoding:deflate” implementation. Here are two HTTP replies that trigger the bug:
The bug allows memory corruption, which can be exploited to execute arbitrary code. The big surprise (to me at least) is that nobody seems to have found this before even though it’s fairly easy to trigger.