CVE-2026-26861

CleverTap Web SDK is vulnerable to DOM-based XSS via handleCustomHtmlPreviewPostMessageEvent function

8.3 HighFix available

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

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: Required

What an attacker can affect

Confidentiality: High
Integrity: High
Availability: Low

Exploit likelihood

0.21%Up 0.2 points since Feb 28, 2026

What each source reports

CVE List Score used 8.3

Record: CVE-2026-26861
CVSS 3.1: 8.3 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L
Weakness: CWE-346
Updated: 2026-11-02

EUVDEUVD-2026-9038 8.3

Record: EUVD-2026-9038
CVSS 3.1: 8.3 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L
Updated: 2026-11-02

GitHub AdvisoriesGHSA-j5mf-6rh3-rhgg 8.3

CleverTap Web SDK is vulnerable to DOM-based XSS via handleCustomHtmlPreviewPostMessageEvent function

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.

Record: GHSA-j5mf-6rh3-rhgg
CVSS 3.1: 8.3 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L
Weakness: CWE-79, CWE-346
Updated: 2026-11-02

NVD 8.3

Record: CVE-2026-26861
CVSS 3.1: 8.3 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L
Weakness: CWE-346
Updated: 2026-11-02

OSV 8.3

Record: CVE-2026-26861
CVSS 3.1: 8.3 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L
Updated: 2026-11-02

OSVGHSA-j5mf-6rh3-rhgg 8.3

CleverTap Web SDK is vulnerable to DOM-based XSS via handleCustomHtmlPreviewPostMessageEvent function

Record: GHSA-j5mf-6rh3-rhgg
CVSS 3.1: 8.3 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L
Weakness: CWE-346, CWE-79
Updated: 2026-11-02

Affected products

clevertap web sdk

Affected packages

Affected packages
Package	Affected	Fixed
`clevertap-web-sdk` npm	before 1.15.3	1.15.3

History

History
Recorded	Changed	Sources
Nov 2, 2026	first indexed	CVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-26861 is a high vulnerability (CVSS 8.3) in Clevertap Web Sdk, published February 27, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.21%, the 10th percentile. Fixed in clevertap-web-sdk 1.15.3.