CVE-2025-21276 in Windows
Summary
by MITRE • 01/14/2025
Windows MapUrlToZone Denial of Service Vulnerability
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Analysis
by VulDB Data Team • 01/14/2025
This vulnerability resides in the Windows operating system's handling of URL mapping to security zones, specifically within the MapUrlToZone function that determines the security level of web resources based on their location. The flaw occurs when the system processes certain malformed or specially crafted URLs that cause the MapUrlToZone function to enter an infinite loop or consume excessive system resources during zone determination. This represents a classic denial of service condition where legitimate system operations become unavailable due to resource exhaustion or execution path manipulation.
The technical implementation issue stems from insufficient input validation within the URL parsing and zone assignment logic. When Windows encounters a malformed URL structure that triggers the MapUrlToZone function, the processing routine fails to properly handle boundary conditions or recursive references in the URL parsing algorithm. This allows an attacker to craft specific URL patterns that cause the system to repeatedly process the same URL components or enter conditional loops that prevent normal execution flow. The vulnerability is particularly concerning because it can be triggered through various user interaction points including web browsers, email clients, and document processing applications that invoke the Windows zone mapping functionality.
Operational impact of this vulnerability extends beyond simple service disruption as it affects the core security infrastructure of Windows systems. When exploited successfully, the denial of service condition prevents legitimate users from accessing web resources or performing zone-based security operations, effectively creating a barrier to normal system functionality. The vulnerability can be particularly dangerous in enterprise environments where automated security policies depend on proper zone assignment for network access control and content filtering. Attackers could leverage this weakness to disrupt business operations, disable security features, or create conditions that facilitate further exploitation attempts.
Mitigation strategies should focus on immediate system updates through Microsoft's regular security patches and Windows updates that address the specific MapUrlToZone implementation flaw. Organizations should implement network-level controls such as web application firewalls and URL filtering systems that can detect and block suspicious URL patterns before they reach vulnerable Windows components. Additional protective measures include configuring security policies to limit zone assignment operations, implementing monitoring solutions that detect unusual resource consumption patterns, and ensuring proper input validation across all applications that interface with Windows zone mapping services. This vulnerability aligns with CWE-400 which covers unchecked resource allocation and ATT&CK technique T1499 for resource exhaustion attacks, emphasizing the need for comprehensive defensive measures across multiple operational layers.