The URL parser in Microsoft Internet Information Services (IIS) 5.1 on Windows XP Professional SP2 allows remote attackers to execute arbitrary code via multiple requests to ".dll" followed by arguments such as "~0" through "~9", which causes ntdll.dll to produce a return value that is not correctly handled by IIS, as demonstrated using "/_vti_bin/.dll/*/~0". NOTE: the consequence was originally believed to be only a denial of service (application crash and reboot).

A carefully crafted If: request header can cause a memory read, or write of a single zero byte, in a pool (heap) memory location beyond the header value sent. This could cause the process to crash. This issue affects Apache HTTP Server 2.4.54 and earlier.

Microsoft Internet Information Services (IIS) 5.1 permits the IUSR_Machine account to execute non-EXE files such as .COM files, which allows attackers to execute arbitrary commands via arguments to any .COM file that executes those arguments, as demonstrated using win.com when it is in a web directory with certain permissions.