CVE-2026-26862 is a DOM-based Cross-Site Scripting (XSS) vulnerability found in the CleverTap Web SDK version 1.15.2 and earlier, specifically within the Visual Builder module. The vulnerability stems from improper origin validation in the source file src/modules/visualBuilder/pageBuilder.js, where the origin URL is checked using the JavaScript includes() method to verify that it contains the string "dashboard.clevertap.com". This approach is insecure because an attacker can craft a malicious subdomain, such as "dashboard.clevertap.com.evil.com", which passes the includes() check but is not a legitimate origin. This bypass allows the attacker to inject and execute arbitrary JavaScript code within the victim's browser context. The attack vector leverages window.postMessage, a browser API used for cross-origin communication, which is mishandled due to the flawed origin validation. Since this is a DOM-based XSS, the malicious script executes on the client side without server-side input validation failures. The vulnerability does not require authentication or user interaction, increasing its risk profile. While no known exploits have been reported in the wild, the vulnerability is publicly disclosed and should be addressed promptly. The lack of a CVSS score necessitates an assessment based on the impact on confidentiality, integrity, and availability, ease of exploitation, and scope of affected systems. CleverTap is widely used for user engagement and analytics in web applications, making this vulnerability relevant to many organizations globally.

The exploitation of this DOM-based XSS vulnerability can lead to the execution of arbitrary JavaScript in the context of affected web applications, potentially compromising user data confidentiality and integrity. Attackers could steal session tokens, manipulate the DOM to perform phishing attacks, or execute malicious actions on behalf of users. This can result in unauthorized access to sensitive information, user impersonation, and erosion of user trust. Since CleverTap is integrated into many web applications for analytics and user engagement, a successful attack could impact a broad user base. The vulnerability does not directly affect availability but can indirectly cause service disruptions through malicious payloads. Organizations using the vulnerable SDK may face reputational damage, regulatory penalties, and financial losses if exploited. The ease of exploitation without authentication or user interaction increases the likelihood of attacks, especially in environments where the SDK is exposed to untrusted origins.

To mitigate this vulnerability, organizations should immediately upgrade to a patched version of the CleverTap Web SDK once available. In the absence of an official patch, developers should implement stricter origin validation by replacing the insecure includes() method with exact origin matching or using robust URL parsing techniques to verify the origin against a whitelist of allowed domains. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts and reduce the impact of XSS attacks. Additionally, sanitize and validate all data received via window.postMessage to ensure it conforms to expected formats and origins. Conduct thorough security testing of the Visual Builder module and related components to detect similar flaws. Monitor application logs and user reports for signs of exploitation attempts. Educate development teams about secure coding practices related to cross-origin communication and DOM-based XSS prevention.