CVE-2025-50864 is a vulnerability in the elysia-cors library, a tool used to enforce Cross-Origin Resource Sharing (CORS) policies in web applications. The vulnerability arises from an origin validation error where the library checks if the origin header supplied by a client is a substring of any domain listed in the CORS whitelist rather than performing an exact domain match. This flawed logic means that malicious origins containing the whitelisted domain as a substring (e.g., 'notexample.com' when 'example.com' is allowed) are erroneously accepted. As a result, attackers can bypass CORS restrictions and perform unauthorized cross-origin requests, potentially accessing sensitive user data or performing actions on behalf of the user. The vulnerability is classified under CWE-178 (Improper Neutralization of Argument Delimiters in a Command) due to improper string matching logic. The CVSS v3.1 base score is 6.5 (medium severity), reflecting network attack vector, low attack complexity, no privileges required, but requiring user interaction. The impact primarily affects data integrity by allowing unauthorized data manipulation or access, though confidentiality impact is not directly indicated. No patches or known exploits are currently available, but the vulnerability poses a significant risk to web applications relying on elysia-cors for CORS enforcement. Organizations should audit their use of this library and validate origin matching logic to prevent exploitation.

For European organizations, this vulnerability can lead to unauthorized access to user data through web applications that rely on the elysia-cors library for enforcing CORS policies. This can compromise the integrity of user sessions and data, potentially allowing attackers to perform actions on behalf of users or steal sensitive information. Given the widespread use of web applications and APIs in sectors such as finance, healthcare, and e-commerce across Europe, exploitation could result in data breaches, regulatory non-compliance (e.g., GDPR violations), reputational damage, and financial losses. The vulnerability does not directly impact availability but can undermine trust in affected services. Since exploitation requires user interaction, phishing or social engineering campaigns could be used to lure victims. The medium severity score suggests a moderate but significant risk that should be addressed promptly to prevent escalation or chaining with other vulnerabilities.

1. Immediately audit all web applications and services using the elysia-cors library to identify affected versions (up to 1.3.0). 2. Implement strict exact-match origin validation logic in CORS policies, avoiding substring or partial matches. 3. If possible, replace or patch the elysia-cors library with a version that correctly validates origins once available. 4. Employ Web Application Firewalls (WAFs) to detect and block suspicious cross-origin requests that do not conform to expected origins. 5. Educate developers and security teams about the risks of improper CORS validation and enforce secure coding practices. 6. Monitor logs for unusual cross-origin requests and user activity that may indicate exploitation attempts. 7. Consider additional security controls such as Content Security Policy (CSP) to limit the impact of CORS bypasses. 8. Prepare incident response plans to quickly address any detected exploitation or data leakage.