CVE-2026-49978 DOMPurify IN_PLACE Sanitization Bypass via Attached Shadow Root Inside <template>.content
DOMPurify fails to sanitize shadow DOM content within templates, allowing attackers to inject malicious scripts that execute when the template is cloned.
- 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-2026-49978?
CVE-2026-49978 is a medium-severity cross-site scripting vulnerability in cure53 DOMPurify, published on 14 Jul 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
DOMPurify is a DOM-only cross-site scripting sanitizer for HTML, MathML, and SVG. Prior to 3.4.7, DOMPurify IN_PLACE sanitization could skip shadow contents attached to an element inside <template>.content, allowing attacker-controlled markup such as event handlers, JavaScript URLs, or scripts to survive and execute when an application cloned and inserted the sanitized template. This issue is fixed in version 3.4.7.
Weakness: CWE-79
Which versions are affected by CVE-2026-49978?
2 open source packages ship an affected version, including dompurify. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
dompurify npm | All versions | 3.4.7 |
dompurify npm | All versions | 3.4.7 |
Products include Cure53 Dompurify.
How do I fix CVE-2026-49978?
Upgrade dompurify to 3.4.7 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-2026-49978 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-49978 exists.
Other vulnerabilities in cure53 DOMPurify
- CVE-2024-47875 DOMPurify nesting-based mXSS
- CVE-2024-48910 DOMPurify vulnerable to tampering by prototype polution
- CVE-2026-47423 DOMPurify XSS via `selectedcontent` re-clone
- CVE-2024-45801 Tampering by prototype polution in DOMPurify
- CVE-2026-49458 DOMPurify: Cross-realm IN_PLACE sanitization leaves executable markup intact via realm-bound `instanceof` checks
Sources
Also known as CLSA-2026-1793120038, DEBIAN-CVE-2026-49978, ECHO-63b6-6bde-ad17, GHSA-rp9w-3fw7-7cwq, MINI-236v-h394-f39q, MINI-7c53-5cwx-j26v and 17 more.