CVE-2018-20744 in Go CORS Handler
Summary
by MITRE
The Olivier Poitrey Go CORS handler through 1.3.0 actively converts a wildcard CORS policy into reflecting an arbitrary Origin header value, which is incompatible with the CORS security design, and could lead to CORS misconfiguration security problems.
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Analysis
by VulDB Data Team • 07/03/2023
The vulnerability identified as CVE-2018-20744 affects the Go CORS handler library developed by Olivier Poitrey, specifically versions through 1.3.0. This issue represents a critical flaw in Cross-Origin Resource Sharing implementation that fundamentally undermines the security model designed to protect web applications from cross-origin attacks. The vulnerability manifests when the library processes wildcard CORS policies and inadvertently reflects arbitrary Origin header values back to clients, creating a dangerous misconfiguration that bypasses intended security boundaries.
The technical flaw resides in how the CORS handler processes Origin header values when a wildcard policy is configured. Instead of properly validating or sanitizing the Origin header, the library actively converts wildcard configurations into reflective behaviors that echo back whatever Origin value is present in the incoming request. This design decision directly violates the core principles of CORS security architecture where Origin validation should be strict and controlled. The implementation essentially allows any arbitrary Origin value to be accepted and reflected back, effectively neutralizing the CORS protection mechanisms that are meant to prevent unauthorized cross-origin access to sensitive resources.
From an operational impact perspective, this vulnerability creates a significant security risk for applications that rely on the Go CORS handler for their cross-origin protection. Attackers can exploit this flaw to bypass CORS restrictions by crafting malicious requests with arbitrary Origin headers, potentially enabling them to perform cross-origin attacks such as cross-site request forgery or data exfiltration. The misconfiguration allows attackers to establish unauthorized cross-origin communication channels that should have been blocked by proper CORS policy enforcement. This vulnerability is particularly dangerous because it affects the fundamental security layer that protects web applications from cross-origin threats, potentially exposing sensitive data and application functionality to unauthorized access.
The security implications of this vulnerability align with CWE-693, which deals with Protection Mechanism Failure, and can be mapped to ATT&CK technique T1213.002 related to Data from Information Repositories. The flaw essentially creates a mechanism failure in the CORS implementation that allows unauthorized access patterns to be established. Organizations using affected versions of this library face a heightened risk of security breaches where attackers can manipulate the Origin header to gain access to resources that should be protected by CORS policies. This vulnerability demonstrates the critical importance of proper input validation and security policy enforcement in web application frameworks, as even a single flawed component can compromise the entire security architecture.
Mitigation strategies for this vulnerability require immediate action to upgrade to patched versions of the Go CORS handler library, as version 1.3.1 and later contain the necessary fixes to properly handle wildcard CORS policies without reflecting arbitrary Origin values. Organizations should conduct comprehensive security reviews of their applications to identify any other components that might be using vulnerable versions of this library. Additionally, security teams should implement monitoring for unusual Origin header patterns and establish proper CORS policy validation mechanisms to detect and prevent similar misconfigurations in other parts of their security infrastructure. The fix implemented in subsequent versions ensures that wildcard CORS policies are properly enforced without the reflective behavior that created this vulnerability, restoring the intended security boundaries for cross-origin resource access.