CVE-2026-26861 CleverTap Web SDK is vulnerable to DOM-based XSS via handleCustomHtmlPreviewPostMessageEvent function
An attacker can execute arbitrary JavaScript in the context of users interacting with the CleverTap Web SDK due to insufficient origin validation in postMessage handling.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-26861?
CVE-2026-26861 is a high-severity cross-site scripting vulnerability in n/a, published on 27 Feb 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
CleverTap Web SDK version 1.15.2 and earlier is vulnerable to Cross-Site Scripting (XSS) via window.postMessage. The handleCustomHtmlPreviewPostMessageEvent function in src/util/campaignRender/nativeDisplay.js performs insufficient origin validation using the includes() method, which can be bypassed by an attacker using a subdomain
Weakness: CWE-346
Which versions are affected by CVE-2026-26861?
2 open source packages ship an affected version, including clevertap-web-sdk. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
clevertap-web-sdk npm | All versions | 1.15.3 |
clevertap-web-sdk npm | All versions | 1.15.3 |
Products include Clevertap Clevertap Web Sdk.
How do I fix CVE-2026-26861?
Upgrade clevertap-web-sdk to 1.15.3 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-26861 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-26861 exists.
Other vulnerabilities in n/a
Sources
Also known as GHSA-j5mf-6rh3-rhgg.