CVE-2017-8700 in ASP.NET Core
Summary
by MITRE
ASP.NET Core 1.0, 1.1, and 2.0 allow an attacker to bypass Cross-origin Resource Sharing (CORS) configurations and retrieve normally restricted content from a web application, aka "ASP.NET Core Information Disclosure Vulnerability".
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Analysis
by VulDB Data Team • 01/23/2021
The vulnerability identified as CVE-2017-8700 represents a critical information disclosure flaw within Microsoft's ASP.NET Core framework affecting versions 1.0, 1.1, and 2.0. This vulnerability specifically targets the Cross-origin Resource Sharing (CORS) configuration mechanism that is fundamental to web application security and browser-based resource access control. The flaw allows malicious actors to circumvent intended access restrictions and obtain sensitive data that should normally be protected by CORS policies. The vulnerability stems from improper validation of CORS headers and request handling within the framework's middleware implementation, creating a pathway for unauthorized data retrieval from web applications that rely on CORS for security boundaries.
The technical implementation of this vulnerability lies in how ASP.NET Core processes CORS preflight requests and response headers. When applications configure CORS policies to restrict access from specific origins, the framework should validate incoming requests against these policies before serving content. However, CVE-2017-8700 demonstrates that under certain conditions, the framework fails to properly enforce these restrictions, allowing requests from unauthorized origins to access resources that should be protected. This occurs particularly when applications use the default CORS policy configuration or when specific combinations of request headers and methods trigger the flawed validation logic. The vulnerability is categorized under CWE-200 as an information disclosure weakness, specifically manifesting as improper access control in web applications. Attackers can exploit this by crafting malicious requests that bypass the normal CORS validation process, effectively creating a tunnel for data exfiltration from applications that depend on CORS for security enforcement.
The operational impact of this vulnerability extends beyond simple data exposure, as it fundamentally undermines the security model that applications rely upon for cross-origin protection. Organizations running affected ASP.NET Core applications face significant risk of unauthorized data access, potentially leading to sensitive information disclosure including user credentials, personal data, financial records, and proprietary business information. The vulnerability affects applications across multiple versions, making it particularly dangerous as it requires comprehensive application updates and patching across different framework versions. Security teams must consider the potential for automated exploitation given the straightforward nature of the attack vector, where malicious actors can easily craft requests to bypass CORS restrictions without requiring advanced technical skills. The impact is especially severe for applications handling regulated data or those in high-risk sectors such as financial services, healthcare, or government services where data protection is paramount.
Mitigation strategies for CVE-2017-8700 require immediate application patching and configuration review to address the underlying CORS validation flaw. Organizations should prioritize updating their ASP.NET Core applications to versions that contain the official security patches released by Microsoft, as these updates correct the improper CORS header handling and validation logic. Additionally, security teams should implement comprehensive monitoring for unauthorized access attempts and review existing CORS configurations to ensure they properly restrict access origins and methods. The implementation of additional security controls such as request rate limiting, IP-based access restrictions, and enhanced logging of CORS-related activities can provide defense-in-depth measures. Organizations should also consider implementing web application firewalls that can detect and block suspicious CORS-related requests, and conduct thorough security assessments to identify any applications that may be vulnerable to similar information disclosure vulnerabilities. This vulnerability aligns with ATT&CK technique T1213 which covers data exploitation through information gathering, emphasizing the need for robust access control mechanisms and proper security configuration management to prevent unauthorized data access in web applications.