CVE-2022-21907 Overview
CVE-2022-21907 is a critical Remote Code Execution (RCE) vulnerability affecting the HTTP Protocol Stack (http.sys) in Microsoft Windows. This wormable vulnerability allows unauthenticated remote attackers to execute arbitrary code at the kernel level by sending specially crafted HTTP requests to affected Windows systems. The vulnerability impacts the core HTTP request processing mechanism used by Internet Information Services (IIS) and other Windows components that leverage the HTTP Protocol Stack.
Critical Impact
Unauthenticated remote attackers can achieve full system compromise with kernel-level code execution, potentially enabling wormable propagation across enterprise networks without user interaction.
Affected Products
- Microsoft Windows 10 (versions 1809, 20H2, 21H1, 21H2) - x86, x64, and ARM64 architectures
- Microsoft Windows 11 (x64 and ARM64 architectures)
- Microsoft Windows Server 2019
- Microsoft Windows Server 2022 and Server version 20H2
Discovery Timeline
- January 11, 2022 - CVE-2022-21907 published to NVD
- November 21, 2024 - Last updated in NVD database
Technical Details for CVE-2022-21907
Vulnerability Analysis
This vulnerability resides in the Windows HTTP Protocol Stack (http.sys), a kernel-mode driver responsible for parsing and processing HTTP requests. The flaw allows attackers to exploit the HTTP trailer support feature, which was introduced in recent Windows versions. When processing maliciously crafted HTTP requests containing specific header configurations, the http.sys driver fails to properly validate input, leading to memory corruption that can be leveraged for arbitrary code execution.
The vulnerability is particularly dangerous because http.sys operates at the kernel level, meaning successful exploitation grants attackers SYSTEM-level privileges. Since the vulnerability can be triggered remotely without authentication and requires no user interaction, it presents an ideal target for wormable attacks that could propagate automatically across networks.
Root Cause
The root cause of CVE-2022-21907 lies in improper input validation within the HTTP Protocol Stack's handling of HTTP request headers. Specifically, the vulnerability is related to the HTTP trailer support feature that was enabled by default on Windows 10 version 2004 and later. The http.sys driver does not adequately sanitize certain header field values, allowing attackers to trigger a use-after-free or buffer overflow condition during request processing.
Attack Vector
The attack vector for CVE-2022-21907 is network-based and requires no privileges or user interaction. An attacker can exploit this vulnerability by:
- Identifying a target system running an affected Windows version with an HTTP service listening (IIS, WinRM, or any application using http.sys)
- Crafting a malicious HTTP request with specially constructed headers designed to trigger the memory corruption condition
- Sending the request to the target server over the network
- Upon successful exploitation, achieving kernel-level code execution with SYSTEM privileges
The vulnerability is particularly concerning because IIS is widely deployed in enterprise environments, and other Windows services also utilize http.sys for HTTP request handling.
The exploitation mechanism involves sending malformed HTTP requests that abuse the trailer support feature in http.sys. When the kernel-mode driver processes these requests, improper bounds checking leads to memory corruption, which can be leveraged for arbitrary code execution. For detailed technical analysis, refer to the Packet Storm Exploit Analysis.
Detection Methods for CVE-2022-21907
Indicators of Compromise
- Unexpected crashes or blue screens (BSOD) related to http.sys driver failures
- Anomalous HTTP traffic patterns with malformed or oversized header values
- Suspicious network connections to port 80/443 with unusual request patterns
- System event logs showing http.sys errors or kernel-mode exceptions
- Unexplained SYSTEM-level process creation following HTTP service activity
Detection Strategies
- Deploy network intrusion detection signatures to identify malformed HTTP requests targeting the trailer support feature
- Monitor for exploitation attempts using HTTP header analysis at network boundaries
- Enable Windows Event Tracing for HTTP.sys to capture detailed request processing information
- Implement application-level firewalls capable of deep packet inspection for HTTP anomalies
Monitoring Recommendations
- Configure SIEM rules to correlate IIS/HTTP service anomalies with potential exploitation indicators
- Monitor for http.sys driver crashes or restarts in Windows System Event Logs
- Establish baseline HTTP traffic patterns and alert on deviations in header sizes or structure
- Enable kernel debugging telemetry on critical servers to capture crash dump data for analysis
How to Mitigate CVE-2022-21907
Immediate Actions Required
- Apply the January 2022 Microsoft security update immediately to all affected systems
- Prioritize patching internet-facing servers running IIS or other HTTP-based services
- Implement network segmentation to limit exposure of vulnerable systems
- Review and audit all systems running Windows 10 1809+, Windows 11, and Windows Server 2019/2022
Patch Information
Microsoft released security patches for CVE-2022-21907 as part of the January 2022 Patch Tuesday update cycle. Organizations should obtain and apply the appropriate patch for their Windows version through Windows Update, Windows Server Update Services (WSUS), or the Microsoft Security Update Guide. Given the critical nature and wormable potential of this vulnerability, immediate patching is strongly recommended for all affected systems.
Workarounds
- Disable HTTP Trailer Support by setting the registry key HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\HTTP\Parameters\EnableTrailerSupport to 0 (DWORD) and restarting the system
- This workaround applies to Windows Server 2019 and Windows 10 version 1809, where the trailer support feature is not enabled by default but may have been manually configured
- Note that this workaround may impact functionality if trailer support is required for specific applications
# Registry modification to disable HTTP Trailer Support (Windows)
# Run in elevated PowerShell or Command Prompt
reg add "HKLM\System\CurrentControlSet\Services\HTTP\Parameters" /v EnableTrailerSupport /t REG_DWORD /d 0 /f
# Restart required for changes to take effect
shutdown /r /t 0
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
