How do I check whether I am affected by CVE-2026-64646?

- Run `next --version` in the project and compare against `16.2.11` (16.x line) or `15.5.21` (15.x line). - Check whether the app uses the App Router and defines at least one Server Action. - Check whether those routes run on the Edge runtime. - Check whether a custom bodySizeLimit is configured for Server Actions.

What is the fix for CVE-2026-64646?

- Upgrade Next.js to `16.2.11` on the 16.x line or `15.5.21` on the 15.x line. - Until patched, set a custom bodySizeLimit for Server Actions; Cloudflare reports no WAF rule covers this issue.

Who is not affected by CVE-2026-64646?

Not affected if: no-server-actions, pages-router.

Live › vulnerability › CVE-2026-64646

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medium6.3Package

Next.js: unbounded Server Action payload lets crafted requests exhaust memory

Next.js App Router apps with at least one Server Action can be sent a crafted request on the Edge runtime that makes the server consume large amounts of memory. The result is a denial of service for the affected process.

Summary written from the sources below. Check the originals before acting.

CVSS 4.0

6.3

medium

scored by [email protected]

known so far5 of 6

missing: exploitation

First public: Jul 21, 2026 UTC
Last modified: Oct 24, 2026
Status: open
Known exploitation: None reported
Public exploit: None on GitHub
EPSS: not scored

First seen by InfraStack 2026-10-24 18:43 UTC, 0h before NVD. All times on this page are UTC.

Why it is medium, and not just CVSS

Likelihood → · Impact ↓

critical

high

medium

high

medium

low

medium

low

Exploited: No reports yet.
Needs login: No.
Needs a special setup: Yes.
Reachable from: internet.
Worst case: Crafted requests exhaust server memory and deny service.
CVSS said: 6.3. The facts above agree.

Who is affected

2 products

Next.js applications from up to , and 16.x releases below , are exposed when they use the App Router with at least one Server Action on the Edge runtime. Apps on the Pages Router or with no Server Actions are not on the affected path. Self-hosted and other deployments should all be checked against the version and feature conditions.

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Product	Ecosystem	Affected	Fixed in
vercel next.js	vendor	>= 13.0.0, < 15.5.21	15.5.21
vercel next.js	vendor	>= 16.0.0, < 16.2.11	16.2.11

Advisory	CVE	Severity	Issue	WAF Coverage
Denial of Service in App Router using Server Actions	CVE-2026-64641	High	Crafted requests targeting Next.js applications using App Router with at least one Server Action can lead to excessive CPU usage. The CPU usage blocks processing of further requests in the same process, leading to Denial of Service.	WAF rule Next.js - DoS - CVE-2026-64641 (...90dcdb0a) has been deployed to provide coverage.
Middleware / Proxy bypass in App Router applications using Turbopack and single locale	CVE-2026-64642	High	Next.js applications using App Router built with Turbopack and a single entry in config.i18n.locales are vulnerable to a middleware/proxy bypass. Accordingly, any authentication or security checks that a middleware/proxy may perform are bypassed.	This is a middleware bypass that unfortunately cannot be covered through Cloudflare WAF signature engine.
Server-Side Request Forgery in rewrites via attacker-controlled destination hostname	CVE-2026-64645	High	A rewrites() or redirects() rule that builds its external destination hostname from request-controlled input can be pointed at an arbitrary hostname, regardless of the rule's hostname suffix. For rewrites, this behavior enables Server-Side Request Forgery (SSRF); for redirects, Open Redirect can be achieved.	Existing SSRF rules provide adequate coverage for this vulnerability, no tailored WAF rule was developed.
Server-Side Request Forgery in Server Actions on custom servers	CVE-2026-64649	High	When a Server Action forwards or redirects a request, an attacker can cause the server to send that outbound request to a malicious host (Server-Side Request Forgery). This requires the attacker’s request to control Host-associated headers.	WAF rule Next.js - SSRF - CVE-2026-64649 (...930091a3) has been deployed to provide coverage.
Denial of Service in the Image Optimization API using SVGs	CVE-2026-64644	Medium	When self-hosting Next.js with the default image loader, the Image Optimization API can optimize remotely hosted images if configured (not enabled by default). If those images contain malicious content, the images can cause CPU exhaustion in the /_next/image endpoint.	Malicious request is unfortunately indistinguishable from a legitimate image optimization request, so no WAF rule has been created to address this vulnerability.
Unbounded Server Action payload in Edge runtime	CVE-2026-64646	Medium	A crafted request can lead to memory consumption on Server Actions in the Edge runtime. Next.js applications which use App Router and have at least one Server Action are affected.	Unfortunately there is no one size fits all rule that can be deployed through WAF in lieu of custom bodySizeLimit configurations, so no WAF rule has been created to address this vulnerability.
Unauthenticated disclosure of internal Server Function endpoints	CVE-2026-64643	Medium	In Next.js applications using App Router, Server Actions (use server) or use cache endpoint IDs can be globally disclosed. An attacker can use this for reconnaissance and as part of a broader attack chain.	WAF rule Next.js - Information Disclosure - CVE-2026-64643 (...72952826) has been deployed to provide coverage.
Cache confusion of response bodies for requests with bodies	CVE-2026-64648	Medium	A server-side fetch with a request body may return a cached response body from a different request to the same URL but different body. This only applies for fetch calls of the shape fetch(new Request(init), aDifferentInit)	This is an application logic bug that unfortunately cannot be covered through Cloudflare WAF signature engine.
Cache confusion of response bodies for requests with bodies containing invalid UTF-8 byte sequences	CVE-2026-64647	Medium	A server-side fetch with a request body may return a cached response body from a different request to the same URL but different body. This only applies when receiving request bodies which contain invalid UTF-8 characters.	This is an application logic bug that unfortunately cannot be covered through Cloudflare WAF signature engine.

Advisory

CVE

Severity

Issue

WAF Coverage

Denial of Service in App Router using Server Actions

CVE-2026-64641

High

Crafted requests targeting Next.js applications using App Router with at least one Server Action can lead to excessive CPU usage. The CPU usage blocks processing of further requests in the same process, leading to Denial of Service.

WAF rule Next.js - DoS - CVE-2026-64641 (...90dcdb0a) has been deployed to provide coverage.

Middleware / Proxy bypass in App Router applications using Turbopack and single locale

CVE-2026-64642

High

Next.js applications using App Router built with Turbopack and a single entry in config.i18n.locales are vulnerable to a middleware/proxy bypass. Accordingly, any authentication or security checks that a middleware/proxy may perform are bypassed.

This is a middleware bypass that unfortunately cannot be covered through Cloudflare WAF signature engine.

Server-Side Request Forgery in rewrites via attacker-controlled destination hostname

CVE-2026-64645

High

A rewrites() or redirects() rule that builds its external destination hostname from request-controlled input can be pointed at an arbitrary hostname, regardless of the rule's hostname suffix. For rewrites, this behavior enables Server-Side Request Forgery (SSRF); for redirects, Open Redirect can be achieved.

Existing SSRF rules provide adequate coverage for this vulnerability, no tailored WAF rule was developed.

Server-Side Request Forgery in Server Actions on custom servers

CVE-2026-64649

High

When a Server Action forwards or redirects a request, an attacker can cause the server to send that outbound request to a malicious host (Server-Side Request Forgery). This requires the attacker’s request to control Host-associated headers.

WAF rule Next.js - SSRF - CVE-2026-64649 (...930091a3) has been deployed to provide coverage.

Denial of Service in the Image Optimization API using SVGs

CVE-2026-64644

Medium

When self-hosting Next.js with the default image loader, the Image Optimization API can optimize remotely hosted images if configured (not enabled by default). If those images contain malicious content, the images can cause CPU exhaustion in the /_next/image endpoint.

Malicious request is unfortunately indistinguishable from a legitimate image optimization request, so no WAF rule has been created to address this vulnerability.

Unbounded Server Action payload in Edge runtime

CVE-2026-64646

Medium

A crafted request can lead to memory consumption on Server Actions in the Edge runtime. Next.js applications which use App Router and have at least one Server Action are affected.

Unfortunately there is no one size fits all rule that can be deployed through WAF in lieu of custom bodySizeLimit configurations, so no WAF rule has been created to address this vulnerability.

Unauthenticated disclosure of internal Server Function endpoints

CVE-2026-64643

Medium

In Next.js applications using App Router, Server Actions (use server) or use cache endpoint IDs can be globally disclosed. An attacker can use this for reconnaissance and as part of a broader attack chain.

WAF rule Next.js - Information Disclosure - CVE-2026-64643 (...72952826) has been deployed to provide coverage.

Cache confusion of response bodies for requests with bodies

CVE-2026-64648

Medium

A server-side fetch with a request body may return a cached response body from a different request to the same URL but different body. This only applies for fetch calls of the shape fetch(new Request(init), aDifferentInit)

This is an application logic bug that unfortunately cannot be covered through Cloudflare WAF signature engine.

Cache confusion of response bodies for requests with bodies containing invalid UTF-8 byte sequences

CVE-2026-64647

Medium

A server-side fetch with a request body may return a cached response body from a different request to the same URL but different body. This only applies when receiving request bodies which contain invalid UTF-8 characters.

This is an application logic bug that unfortunately cannot be covered through Cloudflare WAF signature engine.

Ruleset	Rule ID	Legacy Rule ID	Description	Previous Action	New Action	Comments
Cloudflare Managed Ruleset	...215e7d31	N/A	SSRF - Restricted Protocol	Log	Block	This is a new detection.
Cloudflare Managed Ruleset	...a935ee5d	N/A	SSRF - Obfuscated Host	Log	Block	This is a new detection.
Cloudflare Managed Ruleset	...1b0230ac	N/A	LFI - Path Traversal	Log	Block	This is a new detection.
Cloudflare Managed Ruleset	...61349c8b	N/A	Adobe ColdFusion - File Upload Path Traversal - CVE:CVE-2026-48276	Log

Ruleset

Rule ID

Legacy Rule ID

Description

Previous Action

New Action

Comments

Cloudflare Managed Ruleset

...215e7d31

N/A

SSRF - Restricted Protocol

Log

Block

This is a new detection.

Cloudflare Managed Ruleset

...a935ee5d

N/A

SSRF - Obfuscated Host

Log

Block

This is a new detection.

Cloudflare Managed Ruleset

...1b0230ac

N/A

LFI - Path Traversal

Log

Block

This is a new detection.

Cloudflare Managed Ruleset

...61349c8b

N/A

Adobe ColdFusion - File Upload Path Traversal - CVE:CVE-2026-48276

Log

Next.js: unbounded Server Action payload lets crafted requests exhaust memory

Why it is medium, and not just CVSS

Who is affected

Know the next one before it finds you.

Next.js: unbounded Server Action payload lets crafted requests exhaust memory

Why it is medium, and not just CVSS

Who is affected

Know the next one before it finds you.

How to check

The fix

Who had it, and when

What the sources say, verbatim

Changelog

WAF Release - 2026-07-21

Sources