CVE-2015-1635

CVE-2015-1635 is a remote code execution flaw in HTTP.sys, the kernel-mode HTTP protocol stack component of Microsoft Windows that handles HTTP(S) traffic for IIS and other web-facing Windows roles. A remote, unauthenticated attacker can trigger it by sending specially crafted HTTP requests to a system listening via HTTP.sys, most commonly an internet-facing IIS web server. Successful exploitation yields arbitrary code execution with kernel/system-level privileges on the target server, giving the attacker full control of the host. Any Windows deployment where HTTP.sys is reachable is affected - typically IIS web servers and web-facing roles such as Exchange or WSUS - although the source data does not specify exact version ranges. The flaw is listed in CISA's Known Exploited Vulnerabilities catalog (added 2022-02-10) with a ~100% EPSS probability of exploitation within 30 days, indicating active exploitation; public proof-of-concept code is not noted in the data and ransomware use is unknown.

What to do: Apply Microsoft updates per vendor instructions (this CVE is addressed by the April 2015 MS15-034 bulletin) on every Windows system where HTTP.sys is reachable, prioritizing internet-facing IIS, Exchange, and WSUS hosts. Inventory your environment for systems running web-facing Windows roles and, if patching must be delayed, restrict inbound HTTP/80 and HTTPS/443 from untrusted sources or filter malformed HTTP requests at a front-end proxy/WAF. As a CISA KEV entry, this is a required patch for federal agencies; treat it as urgent everywhere else.