Next.js: Unbounded postponed resume buffering can lead to DoS
Summary
A request containing the next-resume: 1 header (corresponding with a PPR resume request) would buffer request bodies without consistently enforcing maxPostponedStateSize in certain setups. The previous mitigation protected minimal-mode deployments, but equivalent non-minimal deployments remained vulnerable to the same unbounded postponed resume-body buffering behavior.
Impact
In applications using the App Router with Partial Prerendering capability enabled (via experimental.ppr or cacheComponents), an attacker could send oversized next-resume POST payloads that were buffered without consistent size enforcement in non-minimal deployments, causing excessive memory usage and potential denial of service.
Patches
Fixed by enforcing size limits across all postponed-body buffering paths and erroring when limits are exceeded.
Workarounds
If upgrade is not immediately possible:
Block requests containing the next-resume header, as this is never valid to be sent from an untrusted client.
Next.js: null origin can bypass Server Actions CSRF checks
Summary
origin: null was treated as a "missing" origin during Server Action CSRF validation. As a result, requests from opaque contexts (such as sandboxed iframes) could bypass origin verification instead of being validated as cross-origin requests.
Impact
An attacker could induce a victim browser to submit Server Actions from a sandboxed context, potentially executing state-changing actions with victim credentials (CSRF).
Patches
Fixed by treating 'null' as an explicit origin value and enforcing host/origin checks unless 'null' is explicitly allowlisted in experimental.serverActions.allowedOrigins.
Workarounds
If upgrade is not immediately possible:
Add CSRF tokens for sensitive Server Actions.
Prefer SameSite=Strict on sensitive auth cookies.
Do not allow 'null' in serverActions.allowedOrigins unless intentionally required and additionally protected.
React Server Components have multiple Denial of Service Vulnerabilities
Impact
It was found that the fixes to address DoS in React Server Components were incomplete and we found multiple denial of service vulnerabilities still exist in React Server Components.
We recommend updating immediately.
The vulnerability exists in versions 19.0.0, 19.0.1, 19.0.2, 19.0.3, 19.1.0, 19.1.1, 19.1.2, 19.1.3, 19.1.4, 19.2.0, 19.2.1, 19.2.2, 19.2.3 of:
react-server-dom-webpack
react-server-dom-parcel
react-server-dom-turbopack
The vulnerabilities are triggered by sending specially crafted HTTP requests to Server Function endpoints, and could lead to server crashes, out-of-memory exceptions or excessive CPU usage; depending on the vulnerable code path being exercised, the application configuration and application code.
Patches
Fixes were back ported to versions 19.0.4, 19.1.5, and 19.2.4.
If you are using any of the above packages please upgrade to any of the fixed versions immediately.
If your app’s React code does not use a server, your app is not affected by this vulnerability. If your app does not use a framework, bundler, or bundler plugin that supports React Server Components, your app is not affected by this vulnerability.
References
See the blog post for more information and upgrade instructions.
Next.js HTTP request deserialization can lead to DoS when using insecure React Server Components
A vulnerability affects certain React Server Components packages for versions 19.0.x, 19.1.x, and 19.2.x and frameworks that use the affected packages, including Next.js 13.x, 14.x, 15.x, and 16.x using the App Router. The issue is tracked upstream as CVE-2026-23864.
A specially crafted HTTP request can be sent to any App Router Server Function endpoint that, when deserialized, may trigger excessive CPU usage, out-of-memory exceptions, or server crashes. This can result in denial of service in unpatched environments.
Next.js has Unbounded Memory Consumption via PPR Resume Endpoint
A denial of service vulnerability exists in Next.js versions with Partial Prerendering (PPR) enabled when running in minimal mode. The PPR resume endpoint accepts unauthenticated POST requests with the Next-Resume: 1 header and processes attacker-controlled postponed state data. Two closely related vulnerabilities allow an attacker to crash the server process through memory exhaustion:
1. Unbounded request body buffering: The server buffers the entire POST request body into memory using Buffer.concat() without enforcing any size limit, allowing arbitrarily large payloads to exhaust available memory.
2. Unbounded decompression (zipbomb): The resume data cache is decompressed using inflateSync() without limiting the decompressed output size. A small compressed payload can expand to hundreds of megabytes or gigabytes, causing memory exhaustion.
Both attack vectors result in a fatal V8 out-of-memory error (FATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory) causing the Node.js process to terminate. The zipbomb variant is particularly dangerous as it can bypass reverse proxy request size limits while still causing large memory allocation on the server.
To be affected, an application must run with experimental.ppr: true or cacheComponents: true configured along with the NEXT_PRIVATE_MINIMAL_MODE=1 environment variable.
Strongly consider upgrading to 15.6.0-canary.61 or 16.1.5 to reduce risk and prevent availability issues in Next applications.
h3 v1 has Request Smuggling (TE.TE) issue
I was digging into h3 v1 (specifically v1.15.4) and found a critical HTTP Request Smuggling vulnerability.
Basically, readRawBody is doing a strict case-sensitive check for the Transfer-Encoding header. It explicitly looks for "chunked", but per the RFC, this header should be case-insensitive.
The Bug: If I send a request with Transfer-Encoding: ChuNked (mixed case), h3 misses it. Since it doesn't see "chunked" and there's no Content-Length, it assumes the body is empty and processes the request immediately.
This leaves the actual body sitting on the socket, which triggers a classic TE.TE Desync (Request Smuggling) if the app is running behind a Layer 4 proxy or anything that doesn't normalize headers (like AWS NLB or Node proxies).
Vulnerable Code (src/utils/body.ts):
``js
if (
!Number.parseInt(event.node.req.headers["content-length"] || "") &&
!String(event.node.req.headers["transfer-encoding"] ?? "")
.split(",")
.map((e) => e.trim())
.filter(Boolean)
.includes("chunked") // <--- This is the issue. "ChuNkEd" returns false here.
) {
return Promise.resolve(undefined);
}
`
I verified this locally:
Sent a Transfer-Encoding: ChunKed request without a closing 0 chunk.
Express hangs (correctly waiting for data).
h3 responds immediately (vulnerable, thinks body is length 0).
Impact: Since H3/Nuxt/Nitro is often used in containerized setups behind TCP load balancers, an attacker can use this to smuggle requests past WAFs or desynchronize the socket to poison other users' connections.
Fix: Just need to normalize the header value before checking: .map((e) => e.trim().toLowerCase())`
React Router has CSRF issue in Action/Server Action Request Processing
React Router (or Remix v2) is vulnerable to CSRF attacks on document POST requests to UI routes when using server-side route action handlers in Framework Mode, or when using React Server Actions in the new unstable RSC modes.
> [!NOTE]
> This does not impact applications that use Declarative Mode (<BrowserRouter>) or Data Mode (createBrowserRouter/<RouterProvider>).
React Router vulnerable to XSS via Open Redirects
React Router (and Remix v1/v2) SPA open navigation redirects originating from loaders or actions in Framework Mode, Data Mode, or the unstable RSC modes can result in unsafe URLs causing unintended javascript execution on the client. This is only an issue if developers are creating redirect paths from untrusted content or via an open redirect.
> [!NOTE]
> This does not impact applications that use Declarative Mode (<BrowserRouter>).
React Router SSR XSS in ScrollRestoration
A XSS vulnerability exists in in React Router's <ScrollRestoration> API in Framework Mode when using the getKey/storageKey props during Server-Side Rendering which could allow arbitrary JavaScript execution during SSR if untrusted content is used to generate the keys.
> [!NOTE]
> This does not impact applications if developers have disabled server-side rendering in Framework Mode, or if they are using Declarative Mode (<BrowserRouter>) or Data Mode (createBrowserRouter/<RouterProvider>).
React Router has unexpected external redirect via untrusted paths
An attacker-supplied path can be crafted so that when a React Router application navigates to it via navigate(), <Link>, or redirect(), the app performs a navigation/redirect to an external URL. This is only an issue if developers pass untrusted content into navigation paths in their application code.
React Router has XSS Vulnerability
A XSS vulnerability exists in in React Router's meta()/<Meta> APIs in Framework Mode when generating script:ld+json tags which could allow arbitrary JavaScript execution during SSR if untrusted content is used to generate the tag.
> [!NOTE]
> This does not impact applications using Declarative Mode (<BrowserRouter>) or Data Mode (createBrowserRouter/<RouterProvider>).
Next has a Denial of Service with Server Components - Incomplete Fix Follow-Up
It was discovered that the fix for CVE-2025-55184 in React Server Components was incomplete and did not fully mitigate denial-of-service conditions across all payload types. As a result, certain crafted inputs could still trigger excessive resource consumption.
This vulnerability affects React versions 19.0.2, 19.1.3, and 19.2.2, as well as frameworks that bundle or depend on these versions, including Next.js 13.x, 14.x, 15.x, and 16.x when using the App Router. The issue is tracked upstream as CVE-2025-67779.
A malicious actor can send a specially crafted HTTP request to a Server Function endpoint that, when deserialized, causes the React Server Components runtime to enter an infinite loop. This can lead to sustained CPU consumption and cause the affected server process to become unresponsive, resulting in a denial-of-service condition in unpatched environments.
Denial of Service Vulnerability in React Server Components
Impact
It was found that the fix to address CVE-2025-55184 in React Server Components was incomplete and does not prevent a denial of service attack in a specific case.
We recommend updating immediately.
The vulnerability exists in versions 19.0.2, 19.1.3, and 19.2.2 of:
react-server-dom-webpack
react-server-dom-parcel
react-server-dom-turbopack
These issues are present in the patches published on December 11th, 2025.
Patches
Fixes were back ported to versions 19.0.3, 19.1.4, and 19.2.3.
If you are using any of the above packages please upgrade to any of the fixed versions immediately.
If your app’s React code does not use a server, your app is not affected by this vulnerability. If your app does not use a framework, bundler, or bundler plugin that supports React Server Components, your app is not affected by this vulnerability.
References
See the blog post for more information and upgrade instructions.
Next Server Actions Source Code Exposure
A vulnerability affects certain React packages for versions 19.0.0, 19.0.1, 19.1.0, 19.1.1, 19.1.2, 19.2.0, and 19.2.1 and frameworks that use the affected packages, including Next.js 15.x and 16.x using the App Router. The issue is tracked upstream as CVE-2025-55183.
A malicious HTTP request can be crafted and sent to any App Router endpoint that can return the compiled source code of Server Functions. This could reveal business logic, but would not expose secrets unless they were hardcoded directly into Server Function code.
Next Vulnerable to Denial of Service with Server Components
A vulnerability affects certain React packages for versions 19.0.0, 19.0.1, 19.1.0, 19.1.1, 19.1.2, 19.2.0, and 19.2.1 and frameworks that use the affected packages, including Next.js 15.x and 16.x using the App Router. The issue is tracked upstream as CVE-2025-55184.
A malicious HTTP request can be crafted and sent to any App Router endpoint that, when deserialized, can cause the server process to hang and consume CPU. This can result in denial of service in unpatched environments.
Denial of Service Vulnerability in React Server Components
Impact
There is a denial of service vulnerability in React Server Components.
React recommends updating immediately.
The vulnerability exists in versions 19.0.0, 19.0.1 19.1.0, 19.1.1, 19.1.2, 19.2.0 and 19.2.1 of:
react-server-dom-webpack
react-server-dom-parcel
react-server-dom-turbopack
These issues are present in the patches published last week.
Patches
Fixes were back ported to versions 19.0.2, 19.1.3, and 19.2.2.
If you are using any of the above packages please upgrade to any of the fixed versions immediately.
If your app’s React code does not use a server, your app is not affected by this vulnerability. If your app does not use a framework, bundler, or bundler plugin that supports React Server Components, your app is not affected by this vulnerability.
References
See the blog post for more information and upgrade instructions.
Source Code Exposure Vulnerability in React Server Components
Impact
There is a source code exposure vulnerability in React Server Components.
React recommends updating immediately.
The vulnerability exists in versions 19.0.0, 19.0.1 19.1.0, 19.1.1, 19.1.2, 19.2.0 and 19.2.1 of:
react-server-dom-webpack
react-server-dom-parcel
react-server-dom-turbopack
These issues are present in the patches published last week.
Patches
Fixes were back ported to versions 19.0.2, 19.1.3, and 19.2.2.
If you are using any of the above packages please upgrade to any of the fixed versions immediately.
If your app’s React code does not use a server, your app is not affected by this vulnerability. If your app does not use a framework, bundler, or bundler plugin that supports React Server Components, your app is not affected by this vulnerability.
References
See the blog post for more information and upgrade instructions.
React Server Components are Vulnerable to RCE
Impact
There is an unauthenticated remote code execution vulnerability in React Server Components.
We recommend upgrading immediately.
The vulnerability is present in versions 19.0.0, 19.1.0, 19.1.1, and 19.2.0 of:
react-server-dom-webpack
react-server-dom-parcel
react-server-dom-turbopack
Patches
A fix was introduced in versions 19.0.1, 19.1.2, and 19.2.1. If you are using any of the above packages please upgrade to any of the fixed versions immediately.
If your app’s React code does not use a server, your app is not affected by this vulnerability. If your app does not use a framework, bundler, or bundler plugin that supports React Server Components, your app is not affected by this vulnerability.
References
See the blog post for more information and upgrade instructions.
Next.js is vulnerable to RCE in React flight protocol
A vulnerability affects certain React packages<sup>1</sup> for versions 19.0.0, 19.1.0, 19.1.1, and 19.2.0 and frameworks that use the affected packages, including Next.js 15.x and 16.x using the App Router. The issue is tracked upstream as CVE-2025-55182.
Fixed in:
React: 19.0.1, 19.1.2, 19.2.1
Next.js: 15.0.5, 15.1.9, 15.2.6, 15.3.6, 15.4.8, 15.5.7, 16.0.7, 15.6.0-canary.58, 16.1.0-canary.12+
The vulnerability also affects experimental canary releases starting with 14.3.0-canary.77. Users on any of the 14.3 canary builds should either downgrade to a 14.x stable release or 14.3.0-canary.76.
All users of stable 15.x or 16.x Next.js versions should upgrade to a patched, stable version immediately.
<sup>1</sup> The affected React packages are:
react-server-dom-parcel
react-server-dom-turbopack
react-server-dom-webpack
body-parser is vulnerable to denial of service when url encoding is used
Impact
body-parser 2.2.0 is vulnerable to denial of service due to inefficient handling of URL-encoded bodies with very large numbers of parameters. An attacker can send payloads containing thousands of parameters within the default 100KB request size limit, causing elevated CPU and memory usage. This can lead to service slowdown or partial outages under sustained malicious traffic.
Patches
This issue is addressed in version 2.2.1.
