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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
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The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the availability of the system.
Exploitation activity has been observed. Apply available patches or mitigations urgently.
The exploit probability is moderate. The vulnerability is likely to be exploited in the next 30 days.
A proof of concept is available for this vulnerability (1 exploit found).
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