CVE-2023-21687 in Windows
Summary
by MITRE • 02/14/2023
HTTP.sys Information Disclosure Vulnerability
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Analysis
by VulDB Data Team • 03/15/2023
The HTTP.sys information disclosure vulnerability identified as CVE-2023-21687 represents a critical security flaw within the Windows HTTP API subsystem that affects multiple Windows operating systems including Windows 10, Windows 11, Windows Server 2016, Windows Server 2019, and Windows Server 2022. This vulnerability resides in the http.sys kernel-mode driver responsible for handling HTTP requests and responses, making it a fundamental component of Windows web server functionality and network communication. The flaw allows for unauthorized information disclosure when the system processes certain malformed HTTP requests, potentially exposing sensitive data stored in kernel memory regions that should remain protected from user-space access.
The technical mechanism behind this vulnerability involves improper validation of HTTP request headers and parameters during the processing of specific request patterns that trigger memory access violations within the http.sys driver. When a specially crafted HTTP request is sent to a vulnerable Windows system, the driver fails to properly sanitize input parameters, leading to information leakage from kernel memory spaces. This occurs through a combination of buffer overflows, improper bounds checking, and insufficient validation of request structures that result in memory content being inadvertently exposed to remote attackers. The vulnerability is categorized under CWE-200 Information Exposure and specifically relates to CWE-125 Out-of-bounds Read, which allows attackers to read memory contents beyond intended boundaries. The flaw demonstrates characteristics consistent with the ATT&CK technique T1059 Command and Scripting Interpreter, as attackers can leverage this information to gain deeper insights into system memory structures and potentially identify additional attack vectors.
The operational impact of CVE-2023-21687 extends beyond simple information disclosure, as the leaked memory contents may contain sensitive data including authentication tokens, session identifiers, cryptographic keys, or other confidential information that could be exploited by attackers to escalate privileges or conduct further attacks. The vulnerability affects systems running Windows Server with the Web Server role, IIS web servers, and any system that processes HTTP requests through the http.sys driver. Attackers can potentially leverage this information to craft more sophisticated attacks, including privilege escalation attempts, credential harvesting, or system compromise through additional vulnerabilities that become apparent once the memory contents are known. The vulnerability is particularly concerning because it operates at the kernel level, meaning that successful exploitation can provide attackers with extensive access to system resources and potentially full system control. Organizations running vulnerable systems face significant risk of data breaches, system compromise, and potential lateral movement within their networks, as the leaked information can reveal system configurations, memory layouts, and other sensitive operational details.
Mitigation strategies for CVE-2023-21687 should include immediate deployment of Microsoft security updates, which address the underlying validation issues in the http.sys driver through proper bounds checking and input sanitization. Organizations should also implement network segmentation and firewall rules to limit exposure of vulnerable systems to untrusted networks, particularly blocking unnecessary HTTP traffic to affected systems. Additional defensive measures include monitoring for unusual HTTP request patterns that might indicate exploitation attempts, implementing intrusion detection systems to detect potential abuse of this vulnerability, and conducting thorough security assessments to identify systems running vulnerable versions of Windows. The vulnerability highlights the importance of maintaining up-to-date security patches and implementing robust security monitoring practices, as it demonstrates how kernel-level flaws can provide attackers with powerful reconnaissance capabilities that significantly increase the risk of successful exploitation. Regular security audits and vulnerability assessments should include checks for http.sys related configurations and ensure that systems are properly patched and monitored for potential information disclosure threats.