Resource Allocation Without LimitsWeakness · CWE-770

CVE-2026-21710

HIGH · 7.5 CVSS v3.1 Published 2026-03-30

Mitigation only

No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.

See remediation →

84/100

Remediation priority · High

Remotely reachable No privileges Zero-click

Official description

NVD · unedited

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**

Technical summary

dbcve analysis · high confidence

A TypeError uncaught exception occurs in Node.js HTTP servers when a request contains a header named `__proto__` and the application accesses `req.headersDistinct`. This happens because `dest['__proto__']` resolves to `Object.prototype` rather than undefined, causing `.push()` to be called on a non-array object inside a property getter.

MitigationUntil an official Node.js patch is released, wrap all `req.headersDistinct` accesses in try/catch blocks to prevent unhandled exceptions, and consider validating or filtering incoming headers with suspicious names like `__proto__`.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown

From the vector

Attack vector: Network
Complexity: Low
Privileges: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected?

dbcve checks

Work through these to decide whether this CVE applies to you.

Identify Node.js version

Run `node --version` to obtain the exact version of Node.js runtime

Affected if The version falls within the affected range (if known) or is an unpatched version that contains this vulnerability
Locate HTTP server code using req.headersDistinct

Search source code for occurrences of `req.headersDistinct` - this property is accessed in request handlers, middleware, or logging utilities

Affected if The codebase contains any access to `req.headersDistinct` and processes incoming HTTP requests
Verify server accepts external requests

Inspect the HTTP server configuration and routing logic to confirm it processes requests from clients

Affected if The server accepts and processes HTTP requests from external or untrusted sources
Check for header processing logic

Review how incoming request headers are handled, particularly whether custom header names are validated or restricted

Affected if The server does not filter or reject headers with names like `__proto__` before processing

You are affected if your Node.js version contains this vulnerability AND your application uses req.headersDistinct to process HTTP requests that can contain arbitrary header names including `__proto__`.

Generated from the published advisory. Verify against your own configuration.

Remediation

From vendor data

Mitigation available No clean upgrade yet — mitigate in the meantime

Mitigation

Until an official Node.js patch is released, wrap all `req.headersDistinct` accesses in try/catch blocks to prevent unhandled exceptions, and consider validating or filtering incoming headers with suspicious names like `__proto__`.

Have this fixed Scoped from the published advisory

Consultation2.0 h
Implementation4.0 h
Testing2.0 h
Review / QA2.0 h

10.0 hours of engineering $1,780

Get help mitigating

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,848.

Scan for this in your stack

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References

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-21710 in production — separate from our analysis above.

Notes0 Guidelines

Know something about CVE-2026-21710?

The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.

The version that genuinely resolved it — not the one the vendor claimed
A config change or rule that shut the vector down
A gotcha in the upgrade path that cost you an afternoon

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here

Verified mitigations, workarounds, and config changes
Version or environment caveats, and links to real fixes
No weaponised exploit code, or anything meant to cause harm
No spam, self-promotion, credentials, or personal data

At a glance

A fix existsA vendor remedy is published

Severity 7.5 High

Exploit likelihood EPSS, next 30 days 26.4%

Remediation

A high-priority fix

Have this fixed 10 hrs · Moderate

Typical engagement from $1,780

Get a fix See the full breakdown ↓

A high-priority vulnerability. Send your environment and a specialist will scope CVE-2026-21710 and return a fixed quote and timeline.

You’ll deal with our team directly and deploy the reviewed fix to staging first — never straight to production.

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

Check your environment

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

Scan for this in your stack

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Practitioner notes

No notes yet

Official description

Technical summary

CVSS breakdown

Am I affected?

Remediation

References