CVE-2025-51684 in Web SDK
Summary
by MITRE • 07/30/2026
CleverTap Web SDK v1.15.1 is vulnerable to Cross Site Scripting (XSS). The application does not sanitize untrusted data received via window.postMessage before injecting it into the page DOM. An attacker can craft a malicious message that, when processed by renderCustomHtml, results in execution of arbitrary JavaScript in the context of the hosting site.
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Analysis
by VulDB Data Team • 07/31/2026
The CleverTap Web SDK version 1.15.1 contains a critical cross site scripting vulnerability that arises from improper input sanitization within the message handling mechanism. This vulnerability stems from the application's failure to adequately validate and sanitize untrusted data received through the window.postMessage API before incorporating it into the document object model. The flaw specifically manifests in the renderCustomHtml function which processes incoming messages without sufficient security controls, creating an environment where malicious actors can inject harmful scripts that execute within the context of the hosting website.
The technical implementation of this vulnerability demonstrates a classic XSS attack vector through postMessage communication channels. When the SDK receives messages via window.postMessage, it directly incorporates the received data into the DOM structure without proper sanitization or encoding mechanisms. This creates an opportunity for attackers to craft malicious payloads that exploit the lack of input validation in the renderCustomHtml processing function. The vulnerability is particularly dangerous because it operates within the legitimate context of the hosting site, making it difficult to detect and potentially allowing for more sophisticated attacks including session hijacking, data theft, or further exploitation of the victim's browsing session.
The operational impact of this vulnerability extends beyond simple script execution as it provides attackers with the ability to manipulate the entire web application environment. When arbitrary JavaScript executes within the hosting site's context, attackers can potentially access sensitive user data, modify page content, redirect users to malicious sites, or even establish persistent backdoors through browser-based attacks. The vulnerability affects all users of the CleverTap Web SDK version 1.15.1 and can be exploited by any attacker who can send a crafted message to the application via the postMessage API. This creates a particularly concerning scenario where legitimate communication channels become attack vectors, as the vulnerability leverages the very mechanisms designed for secure cross-origin communication.
Security mitigations for this vulnerability should focus on implementing comprehensive input validation and output encoding strategies throughout the SDK's message handling pipeline. The recommended approach involves sanitizing all incoming data from window.postMessage before any DOM insertion occurs, utilizing established XSS prevention libraries or frameworks that properly encode special characters and validate content against known safe patterns. Organizations using the affected SDK version should immediately upgrade to a patched release that implements proper data sanitization techniques and incorporates security controls aligned with CWE-79 which specifically addresses cross site scripting vulnerabilities. Additionally, implementing content security policies and monitoring for unauthorized postMessage communications can provide additional defense in depth measures to protect against exploitation attempts.
The vulnerability demonstrates a failure in secure coding practices that aligns with ATT&CK technique T1211 which covers the use of malicious code injection methods. This weakness represents a common pattern where developers assume that legitimate API calls cannot be abused, but fail to implement proper security controls around data flow between components. The issue also reflects poor adherence to the principle of least privilege and input validation requirements typically enforced by security frameworks such as the OWASP Top Ten and NIST cybersecurity guidelines. Organizations should conduct thorough code reviews focusing on message handling mechanisms and ensure that all external inputs are properly validated before being processed or rendered within web applications.