CVE-2026-21710: A flaw in Node.js HTTP request handling causes an uncaught `TypeError` when a request is received with a header named `__proto__` and the application accesses `req.headersDistinct`.
When this occurs, `dest["__proto__"]` resolves to `Object.prototype` rather than `undefined`, causing `.push()` to be called on a non-array. This exception is thrown synchronously inside a property getter and cannot be intercepted by `error` event listeners, meaning it cannot be handled without wrapping every `req.headersDistinct` access in a `try/catch`.
* This vulnerability affects all Node.js HTTP servers on **20.x, 22.x, 24.x, and v25.x**
Overview
- Severity
- High (CVSS 7.5)
- CVSS Vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Exploit Status
- Not Exploited
- Patch Tuesday
- 2026-Mar
- Released
- 2026-04-01
- Last Updated
- 2026-04-09
- EPSS Score
- 26.36% (percentile: 97.7%)
Affected Products (3)
Other
Open Source Software
- azl3 nodejs24 24.13.0-3 on Azure Linux 3.0
Revision History
- 2026-04-01: Information published.
- 2026-04-08: Information published.
- 2026-04-09: Information published.