# CVE-2026-41240: DOMPurify: FORBID_TAGS bypassed by function-based ADD_TAGS predicate (asymmetry with FORBID_ATTR fix)

Source: https://junglewise.ai/threats/cve-2026-41240-dompurify-forbid-tags-bypassed-by-function-based-add-tags  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-23. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-41240 · Severity: medium · CVSS 6.1 · Published 2026-04-23

DOMPurify is a widely-used JavaScript HTML sanitization library that removes potentially dangerous content from user-supplied HTML. A configuration inconsistency allows attackers to bypass tag blocking rules when using function-based tag allowlists, potentially injecting malicious iframe, form, and other elements with external URLs. This could enable credential theft, data exfiltration, and XSS attacks in applications that rely on FORBID_TAGS to block dangerous elements.

Technologies: [Cure53 DOMPurify](https://junglewise.ai/threats/technologies/cure53-dompurify), [dompurify (npm)](https://junglewise.ai/threats/technologies/dompurify). Vendors: [Cure53](https://junglewise.ai/threats/vendors/cure53), [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2026-41240 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-41240 being exploited in the wild.

**How severe is CVE-2026-41240?** Medium severity, with a CVSS score of 6.1, published 23 April 2026.

**Which products and versions are affected?** dompurify (npm) < 3.4.0, SEMVER:introduced=0,fixed=3.4.0.

**Is there a fix for CVE-2026-41240?** Yes. dompurify (npm): upgrade to 3.4.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-41240 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-41240?** Check whether you run Cure53 DOMPurify or dompurify (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- dompurify (npm): upgrade to 3.4.0 or later

  ```sh
  npm install dompurify@3.4.0
  ```


## Technical details

This vulnerability is a logic bypass (CWE-183) in DOMPurify's tag sanitization flow. The root cause is asymmetric handling of FORBID_TAGS and ADD_TAGS: a prior fix (commit c361baa) added an early exit for FORBID_ATTR before checking ADD_ATTR, but the same logic was not applied to tags. When EXTRA_ELEMENT_HANDLING.tagCheck is a function that returns true, short-circuit evaluation in the conditional at lines 1118–1123 skips the FORBID_TAGS check entirely, allowing forbidden tags like iframe, form, object, and embed to pass through with their attributes intact. The vulnerability requires a function-based ADD_TAGS predicate in the configuration (uncommon but legitimate usage). An attacker who controls the sanitizer configuration and input HTML can inject dangerous elements; impact depends on the application context but includes XSS, phishing (form injection), and data theft (iframe with external action/src).

## Affected products

- Cure53 DOMPurify <= 3.2.6

## Identifiers

- CVE-2026-41240
- GHSA-h7mw-gpvr-xq4m

## Timeline

- 2026-04-22: disclosed: Advisory published
- 2026-04-20: patched: Fix released in version 3.4.0

## References

- [https://github.com/cure53/DOMPurify/security/advisories/GHSA-h7mw-gpvr-xq4m](https://github.com/cure53/DOMPurify/security/advisories/GHSA-h7mw-gpvr-xq4m)

## Related threats

- [DOMPurify SAFE_FOR_TEMPLATES bypass via shadow root content](https://junglewise.ai/threats/cve-2026-116804-dompurify-from-3-4-4-before-3-4-17-contains-a-safe-for-templates)
- [DOMPurify DOM XSS in IN_PLACE hook-detached subtrees](https://junglewise.ai/threats/cve-2026-116803-dompurify-before-3-4-17-contains-a-cross-site-scripting)
- [DOMPurify cross-site scripting in SMIL attributeName guard bypass](https://junglewise.ai/threats/cve-2026-116802-dompurify-before-3-4-17-contains-a-cross-site-scripting)
- [DOMPurify SAFE_FOR_TEMPLATES bypass in shadow root content](https://junglewise.ai/threats/dompurify-safe-for-templates-bypass-split-template-expressions-survive-c23665cf)
- [DOMPurify IN_PLACE event handler bypass when hook removes parent or sibling](https://junglewise.ai/threats/dompurify-in-place-hook-that-removes-a-parent-or-sibling-leaves-the-3ea5d18f)