HIGH 7.5 Microsoft

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**

Microsoft Security Update 2026-Aug: 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**

Affected Products

References

Published: 2026-08-06 · Source: Microsoft · Feed updated: 2026-08-10
This high severity vulnerability with a CVSS score of 7.5 was published on 2026-08-06 via Microsoft. EPSS score: 26.4% (top 2% of all CVEs by exploitation probability). Affected: cbl2 nodejs18 18.20.3-12, cbl2 nodejs18 18.20.3-12 on CBL Mariner 2.0, azl3 nodejs 20.14.0-14 on Azure Linux 3.0 and 1 more.
vulnfeed aggregates 9044 vulnerabilities from NVD, CISA KEV, Ubuntu, Debian, Red Hat, Kubernetes, Exploit-DB, OSS-Security, GitHub and OpenStack — updated every 4 hours.