CVE-2025-56200 is a vulnerability in the popular JavaScript validation library validator.js, specifically affecting versions up to 13.15.15. The vulnerability arises from the isURL() function's URL parsing logic. This function uses the delimiter '://' to separate the protocol from the rest of the URL, whereas modern browsers use ':' as the delimiter. This discrepancy allows attackers to craft malicious URLs that bypass the protocol and domain validation checks performed by isURL(). Consequently, attackers can inject URLs that appear valid to the validator but are interpreted differently by browsers. This parsing mismatch can be exploited to conduct Cross-Site Scripting (XSS) attacks and Open Redirect attacks. XSS attacks can lead to the execution of arbitrary scripts in the context of the victim's browser, potentially stealing sensitive information or performing actions on behalf of the user. Open Redirect vulnerabilities can be abused to redirect users to malicious sites, facilitating phishing or malware distribution. The vulnerability does not currently have a CVSS score, and no known exploits in the wild have been reported. However, given the widespread use of validator.js in web applications for input validation, this vulnerability poses a significant risk if unpatched. The lack of patch links suggests that a fix may not yet be publicly available or that users must update to a later version beyond 13.15.15 once released.

For European organizations, this vulnerability can have serious implications. Many web applications and services rely on validator.js for input validation, including those handling sensitive personal data protected under GDPR. Successful exploitation could lead to XSS attacks, compromising user sessions, stealing credentials, or injecting malicious content, thereby violating data protection regulations and damaging organizational reputation. Open Redirects can facilitate phishing campaigns targeting European users, increasing the risk of credential theft and fraud. Sectors such as finance, healthcare, e-commerce, and government services, which heavily rely on web applications, are particularly at risk. The impact extends to both confidentiality and integrity of data, as well as availability if attacks lead to service disruption or blacklisting by browsers and security tools. Additionally, regulatory fines and legal consequences could arise from breaches caused by exploitation of this vulnerability.

European organizations should immediately audit their use of validator.js and identify all instances where isURL() is employed for URL validation. Until an official patch is released, developers should implement custom URL validation logic that aligns with browser parsing rules, specifically using ':' as the protocol delimiter rather than '://'. Employing additional layers of input sanitization and output encoding can reduce the risk of XSS. Web Application Firewalls (WAFs) should be configured to detect and block suspicious URL patterns that exploit this parsing discrepancy. Organizations should monitor security advisories from the validator.js maintainers and plan prompt upgrades to patched versions once available. Security teams should also conduct penetration testing focused on URL validation to identify potential exploit vectors. User education on phishing risks related to open redirects can further mitigate impact. Finally, implementing Content Security Policy (CSP) headers can limit the damage caused by XSS attacks.