CVE-2020-0645 in IIS
Summary
by MITRE
A tampering vulnerability exists when Microsoft IIS Server improperly handles malformed request headers, aka 'Microsoft IIS Server Tampering Vulnerability'.
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Analysis
by VulDB Data Team • 04/10/2024
The CVE-2020-0645 vulnerability represents a critical tampering flaw within Microsoft Internet Information Services (IIS) server implementations that stems from improper handling of malformed request headers. This vulnerability specifically affects IIS versions 7.0 through 10.0 and exists at the protocol level where the server fails to properly validate and sanitize incoming HTTP request headers before processing them. The flaw manifests when IIS encounters malformed headers that contain unexpected characters or structures that the server's parsing logic cannot adequately handle, creating opportunities for attackers to manipulate the server's behavior through carefully crafted requests. This type of vulnerability falls under the CWE-129 category of Improper Validation, specifically addressing inadequate input validation in web server components that process HTTP requests.
The technical exploitation of this vulnerability occurs through the manipulation of HTTP request headers during the server's request parsing phase. When IIS receives requests containing malformed headers, the server's internal processing logic may interpret these headers incorrectly, leading to unexpected behavior in the request handling pipeline. Attackers can leverage this by crafting specific header values that cause the server to deviate from its normal processing flow, potentially enabling them to bypass security controls, manipulate application logic, or access restricted resources. The vulnerability's impact is particularly concerning because it operates at the foundational level of HTTP request processing where many security mechanisms depend on proper header validation. This aligns with ATT&CK technique T1071.004 for Application Layer Protocol: DNS, where attackers manipulate protocol elements to achieve unauthorized access or control.
The operational impact of CVE-2020-0645 extends beyond simple request manipulation to potentially enable more sophisticated attack vectors including privilege escalation, data exfiltration, and service disruption. Servers vulnerable to this flaw may experience inconsistent behavior when processing legitimate requests, potentially leading to application crashes or unexpected state changes that could be exploited by attackers. The vulnerability's persistence across multiple IIS versions makes it particularly dangerous for organizations with legacy systems or those that have not yet completed their upgrade cycles. Organizations running IIS servers without proper patch management protocols are at heightened risk, as the vulnerability can be exploited without requiring authentication or specialized attack tools. The flaw's nature means that even basic web traffic could potentially be leveraged for malicious purposes, making it a significant concern for any organization relying on IIS for web services.
Mitigation strategies for CVE-2020-0645 should prioritize immediate patch deployment from Microsoft, specifically targeting the security updates released in the April 2020 security bulletin. Organizations should implement comprehensive monitoring solutions to detect anomalous header patterns that may indicate exploitation attempts, focusing on unusual characters or structures in HTTP headers. Network-level controls including web application firewalls and intrusion detection systems can provide additional protection by filtering malformed headers before they reach the IIS server. Configuration hardening measures should include implementing strict header validation rules and disabling unnecessary HTTP methods that might exacerbate the vulnerability. Security teams should also consider implementing automated patch management processes to ensure timely deployment of security updates across all IIS installations. The vulnerability's classification as a tampering issue underscores the importance of maintaining integrity checks throughout the request processing pipeline, with particular attention to how IIS handles header validation and error recovery mechanisms that could be exploited to maintain persistent access to affected systems.