CVE-2026-41238
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedDOMPurify is a DOM-only cross-site scripting sanitizer for HTML, MathML, and SVG. Versions 3.0.1 through 3.3.3 are vulnerable to a prototype pollution-based XSS bypass. When an application uses `DOMPurify.sanitize()` with the default configuration (no `CUSTOM_ELEMENT_HANDLING` option), a prior prototype pollution gadget can inject permissive `tagNameCheck` and `attributeNameCheck` regex values into `Object.prototype`, causing DOMPurify to allow arbitrary custom elements with arbitrary attributes — including event handlers — through sanitization. Version 3.4.0 fixes the issue.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceDOMPurify versions 3.0.1-3.3.3 contain a prototype pollution-based XSS bypass. When CUSTOM_ELEMENT_HANDLING is not configured, a prior prototype pollution gadget can inject permissive regex values into Object.prototype for tagNameCheck and attributeNameCheck, causing DOMPurify to permit arbitrary custom elements with event handlers through sanitization.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- High
- Privileges
- None
- User interaction
- Required
- Scope
- Changed
- Confidentiality
- High
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify DOMPurify versionCheck your package.json, node_modules/dompurify/package.json, or the script source for the DOMPurify version string (e.g., 3.0.x, 3.1.x, 3.2.x, 3.3.x).Affected if The installed version falls within 3.0.1 through 3.3.3 inclusive.
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Verify CUSTOM_ELEMENT_HANDLING configurationSearch your codebase for CUSTOM_ELEMENT_HANDLING configuration in DOMPurify initialization (e.g., DOMPurify.sanitize(dirty, {CUSTOM_ELEMENT_HANDLING: ...})).Affected if CUSTOM_ELEMENT_HANDLING is not defined or not configured in your DOMPurify setup.
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Detect prototype pollution in applicationAudit your JavaScript codebase for vulnerable patterns that allow setting properties on Object.prototype (e.g., recursive merge functions, dynamic property assignment without validation). Look for code that processes untrusted JSON objects.Affected if Your application contains exploitable prototype pollution gadgets that could inject values into Object.prototype.
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Inspect runtime prototype stateAt runtime in your application context, check if Object.prototype has been modified: console.log(Object.prototype.tagNameCheck) and console.log(Object.prototype.attributeNameCheck).Affected if Object.prototype.tagNameCheck or Object.prototype.attributeNameCheck exist as enumerable properties with permissive regex values.
You are affected if DOMPurify 3.0.1-3.3.3 is in use without CUSTOM_ELEMENT_HANDLING configured AND your application has an exploitable prototype pollution vulnerability that could inject into Object.prototype.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedUpgrade DOMPurify to version 3.4.0 or later. Additionally, audit the application for existing prototype pollution vulnerabilities that could serve as the prerequisite gadget for this bypass.
3.4.0
- Identify the current DOMPurify version in your project by checking package.json or package-lock.json
- Update DOMPurify to version 3.4.0 or later using your package manager (e.g., npm install [email protected], yarn add [email protected], or pip install if using a Python wrapper)
- After upgrading, run your project's test suite to verify that sanitization continues to work as expected
- If you have custom sanitization configurations, review them to ensure compatibility with the new version
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation2.0 h
- Testing4.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2026-41238 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-41238 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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