Microsoft Windows HTTP.sys Remote Code Execution Vulnerability (CVE-2015-1635, MS15-034) Technical Analysis and Mitigation Guide

1. Vulnerability Overview & Root Cause

This vulnerability (CVE-2015-1635, also known as MS15-034) is an integer overflow vulnerability within HTTP.sys, the kernel-mode driver responsible for processing HTTP requests in Windows operating systems. The root cause lies in the improper validation of the HTTP Range header. When HTTP.sys parses a request containing an extremely large byte range (e.g., bytes=0-18446744073709551615), an integer overflow occurs during the internal buffer size calculation. This leads to kernel memory corruption when the driver attempts to process the invalid range.

2. Exploitation Mechanics & Attack Scenario

An attacker can exploit this vulnerability remotely without authentication by sending a crafted HTTP GET request.

• Reconnaissance: The attacker sends a request containing Range: bytes=18-18446744073709551615. If the server responds with 'Requested Range Not Satisfiable', it indicates that the system is unpatched and vulnerable.
• Exploitation: To achieve Remote Code Execution (RCE), the attacker crafts a precise payload designed to overwrite kernel memory structures. Because HTTP.sys runs in kernel space, successful exploitation grants the attacker full SYSTEM-level privileges, bypassing all user-mode security controls.
• Denial of Service (DoS): If the exploit payload is unstable or designed for disruption, it triggers a kernel panic, resulting in an immediate Blue Screen of Death (BSOD) and system crash.

3. Infrastructure & Business Impact

With a CVSS score of 9.8, active exploitation history (CISA KEV), and an EPSS score of 1.0, this vulnerability represents an extreme risk to enterprise environments. Compromise of an IIS-based web server or Active Directory Federation Services (ADFS) server can lead to full domain compromise, lateral movement, ransomware deployment, and catastrophic business downtime.