Componentpedia / Listings / next / 15.3.1

A specially crafted HTTP request can be sent to any App Router Server Function endpoint that, when deserialized, may trigger excessive CPU usage. This can result in denial of service in unpatched environments.

Applications that use beforeInteractive scripts together with untrusted content can be vulnerable to cross-site scripting. In affected versions, serialized script content was not escaped safely before being embedded into the document, which could allow attacker-controlled input to break out of the intended script context and execute arbitrary JavaScript in a visitor's browser.

Self-hosted applications using the built-in Node.js server can be vulnerable to server-side request forgery through crafted WebSocket upgrade requests. An attacker can cause the server to proxy requests to arbitrary internal or external destinations, which may expose internal services or cloud metadata endpoints. Vercel-hosted deployments are not affected.

The default Next.js image optimization disk cache (/_next/image) did not have a configurable upper bound, allowing unbounded cache growth.

A cache poisoning issue in Next.js App Router >=15.3.0 and < 15.3.3 may have allowed RSC payloads to be cached and served in place of HTML, under specific conditions involving middleware and redirects. This issue has been fixed in Next.js 15.3.3.

App Router applications that rely on CSP nonces can be vulnerable to stored cross-site scripting when deployed behind shared caches. In affected versions, malformed nonce values derived from request headers could be reflected into rendered HTML in an unsafe way, allowing an attacker to poison cached responses and cause script execution for later visitors.

Applications using Partial Prerendering through the Cache Components feature can be vulnerable to connection exhaustion through crafted POST requests to a server action. In affected configurations, a malicious request can trigger a request-body handling deadlock that leaves connections open for an extended period, consuming file descriptors and server capacity until legitimate users are denied service.

App Router applications that rely on middleware or proxy-based checks for authorization can allow unauthorized access through transport-specific route variants used for segment prefetching. In affected configurations, specially crafted .rsc and segment-prefetch URLs can resolve to the same page without being matched by the intended middleware rule, which can allow protected content to be reached without the expected authorization check.

Strongly consider upgrading to 15.5.10 and 16.1.5 to reduce risk and prevent availability issues in Next applications.

Next.js uses the x-nextjs-data request header for internal data requests. On affected versions, an external client could send this header on a normal request to a path handled by middleware that returns a redirect.

Applications using React Server Components can be vulnerable to cache poisoning when shared caches do not correctly partition response variants. Under affected conditions, an attacker can cause an RSC response to be served from the original URL and poison shared cache entries so later visitors receive component payloads instead of the expected HTML.

A specially crafted HTTP request can be sent to any App Router Server Function endpoint that, when deserialized, may trigger excessive CPU usage. This can result in denial of service in unpatched environments.

All users implementing custom middleware logic in self-hosted environments are strongly encouraged to upgrade and verify correct usage of the next() function.

When self-hosting Next.js with the default image loader, the Image Optimization API fetches local images entirely into memory without enforcing a maximum size limit. An attacker could cause out-of-memory conditions by requesting large local assets from the /_next/image endpoint that match the images.localPatterns configuration (by default, all patterns are allowed).

When Next.js rewrites proxy traffic to an external backend, a crafted DELETE/OPTIONS request using Transfer-Encoding: chunked could trigger request boundary disagreement between the proxy and backend. This could allow request smuggling through rewritten routes.

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+

All users are encouraged to upgrade if they use API routes to serve images that depend on request headers and have image optimization enabled.

All users relying on images.domains or images.remotePatterns are encouraged to upgrade and verify that external image sources are strictly validated.

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.

React Server Component responses can be vulnerable to cache poisoning in deployments that rely on shared caches with insufficient response partitioning. In affected conditions, collisions in the _rsc cache-busting value can allow an attacker to poison cache entries so users receive the wrong response variant for a given URL.

Applications using the Pages Router with i18n configured and middleware/proxy-based authorization can allow unauthorized access to protected page data through locale-less /_next/data/<buildId>/<page>.json requests. In affected configurations, middleware does not run for the unprefixed data route, allowing an attacker to retrieve SSR JSON for protected pages without passing the intended authorization checks.

It was found that the fix addressing CVE-2026-44575 did not apply to middleware.ts with Turbopack. Refer to CVE-2026-44575 for further details.