CVE-2024-6221 in flask-cors
Summary
by MITRE • 08/18/2024
A vulnerability in corydolphin/flask-cors version 4.0.1 allows the `Access-Control-Allow-Private-Network` CORS header to be set to true by default, without any configuration option. This behavior can expose private network resources to unauthorized external access, leading to significant security risks such as data breaches, unauthorized access to sensitive information, and potential network intrusions.
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Analysis
by VulDB Data Team • 07/04/2025
The vulnerability identified as CVE-2024-6221 affects the corydolphin/flask-cors library version 4.0.1, which is a widely used python package for handling cross-origin resource sharing in flask applications. This particular flaw represents a critical security oversight in the default configuration behavior of the cors implementation. The issue stems from the library's automatic setting of the Access-Control-Allow-Private-Network header to true without providing developers with any mechanism to disable this behavior, creating an inherent security risk within applications that utilize this dependency.
The technical flaw manifests through the improper default configuration of the Access-Control-Allow-Private-Network CORS header, which is designed to enable browsers to make requests to private network resources from cross-origin contexts. When this header is set to true by default, it effectively allows external domains to access private network resources that would normally be restricted. This behavior violates fundamental security principles of network segmentation and access control, as it removes the necessary barriers that typically protect internal network resources from unauthorized external access. The vulnerability specifically aligns with CWE-284, which addresses improper access control, and represents a privilege escalation issue within the context of web application security.
The operational impact of this vulnerability is severe and far-reaching for organizations using affected flask applications. Applications that rely on flask-cors for handling cross-origin requests become susceptible to attacks where external malicious actors can potentially access internal network resources that should remain protected. This exposure can lead to data breaches involving sensitive information, unauthorized access to backend services, and potential lateral movement within network infrastructures. The vulnerability creates a pathway for attackers to exploit the trust relationships established by CORS headers, effectively bypassing network security controls that would normally prevent such access. This risk is particularly pronounced in environments where flask applications serve as API endpoints that interact with internal databases or services that are not properly secured against cross-origin requests.
Organizations should immediately implement mitigations to address this vulnerability by updating to the latest version of the flask-cors library where the default behavior has been corrected. Additionally, developers should review their application configurations to ensure that the Access-Control-Allow-Private-Network header is explicitly set to false when private network access is not required. Security teams should monitor their applications for any unauthorized access patterns that might indicate exploitation attempts. The ATT&CK framework categorizes this vulnerability under T1190 - Exploit Public-Facing Application, as it represents an attack surface that can be leveraged to gain access to internal network resources. Organizations should also consider implementing network segmentation controls and monitoring for unusual CORS header behaviors to detect potential exploitation attempts. The vulnerability underscores the importance of proper security configuration management and the need for regular dependency updates to maintain robust security postures.