CVE-2020-1476 in .NET Framework
Summary
by MITRE
An elevation of privilege vulnerability exists when ASP.NET or .NET web applications running on IIS improperly allow access to cached files. An attacker who successfully exploited this vulnerability could gain access to restricted files. To exploit this vulnerability, an attacker would need to send a specially crafted request to an affected server. The update addresses the vulnerability by changing how ASP.NET and .NET handle requests.
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Analysis
by VulDB Data Team • 02/23/2026
The vulnerability described in CVE-2020-1476 represents a critical elevation of privilege flaw within ASP.NET and .NET web applications operating on Internet Information Services platforms. This weakness stems from improper handling of cached file access controls, creating a scenario where authenticated attackers can bypass legitimate access restrictions to gain unauthorized access to restricted system resources. The vulnerability specifically impacts applications that utilize ASP.NET or .NET frameworks when deployed on IIS servers, making it particularly relevant to enterprise web environments that rely heavily on Microsoft technologies.
The technical mechanism underlying this vulnerability involves the flawed implementation of cached file access validation within the ASP.NET and .NET runtime environments. When applications process requests, they maintain cached versions of resources to improve performance, but the vulnerability occurs in how these cached elements are validated against access control policies. Attackers can exploit this by crafting specific HTTP requests that manipulate the caching mechanism, effectively bypassing the normal authentication and authorization checks that should prevent unauthorized access to sensitive files. This type of vulnerability falls under CWE-284, which specifically addresses improper access control issues, and demonstrates how caching mechanisms can inadvertently create security weaknesses when not properly integrated with access control validation.
The operational impact of this vulnerability extends beyond simple data theft, as it provides attackers with elevated privileges that could enable further compromise of the affected systems. Successful exploitation allows attackers to access restricted files that may contain sensitive information such as configuration data, user credentials, application source code, or other confidential resources. The attack requires only a specially crafted request, making it relatively easy to exploit and potentially allowing for automated scanning and exploitation across multiple targets. This vulnerability particularly affects organizations running legacy or improperly configured IIS environments where ASP.NET and .NET applications are deployed without proper security hardening measures.
Microsoft addressed this vulnerability through a comprehensive update that modifies the fundamental way ASP.NET and .NET handle incoming requests and cached file access validation. The fix implements stricter access control checks during request processing, ensuring that cached resources are properly validated against current user permissions before being served. Organizations should prioritize applying this security update immediately, as the vulnerability can be exploited remotely without requiring any special privileges or user interaction beyond sending a malicious request. Security teams should also conduct thorough assessments of their IIS environments to identify any applications that may be running on affected versions of the framework and ensure proper configuration of caching mechanisms to prevent similar issues from occurring in other components of their web infrastructure.