Windows Patch Tuesday Hole Being Used in Zero-Day Attacks
Just one day after Microsoft released its monthly security patch, attackers had already reverse-engineered one of the bulletins and have been using it in active attacks.
According to security training firm SANS Institute, bulletin MS15-034, which resolved an issue in Windows and how it receives HTTP requests (but was not seen in the wild being used in active exploits), had been spotted in its honeypot monitoring to be used in targeted attacks against Web servers.
"The problem is that this will easily crash systems," said SANS Internet Storm Center CTO Johannes Ullrich. "It is not a denial of service, and not easily a data leakage issue like Heartbleed. But even crashing millions of IIS servers could cause significant impact, as many large sites use IIS."
System crashes can occur when the Range header in an HTTP request is manipulated to a variable that is too high for a server to handle, causing a Windows kernel crash. The flaw can be found in Windows 7, 8, 8.1, Windows Server 2008 R2, Windows Server 2012 and Windows Server 2012 R2, which all run Internet Information Services (IIS) for Windows.
SANS Institute has also shared information on how to easily check a IIS server to see if it is vulnerable in a security bulletin. Send the following request through IIS for Windows:
GET / HTTP/1.1
"If the server responds with 'Requested Header Range Not Satisfiable,' then you may be vulnerable," wrote SANS Institute.
The easiest solution is to apply the fix released on Tuesday as soon as possible. Furthermore, if more testing of April's patch is needed before applying it, Microsoft said a workaround is available if the IIS kernel caching is disabled. However, the company warns that performance issues may occur by doing this.