Find, fix and prevent vulnerabilities in your code.

Overview

next is a react framework.

Affected versions of this package are vulnerable to Allocation of Resources Without Limits or Throttling due to the lack of an upper bound on the disk cache used by the image optimization. An attacker can exhaust disk storage by generating a large number of unique image optimization variants, leading to service disruption.

Workaround

This vulnerability can be mitigated by periodically cleaning the .next/cache/images directory or by reducing the number of possible image variants through configuration of images.localPatterns, images.remotePatterns, and images.qualities.

Remediation

Upgrade next to version 16.1.7, 16.2.0-canary.54 or higher.

References

• GitHub Commit
• GitHub Release

Overview

next is a react framework.

Affected versions of this package are vulnerable to Acceptance of Extraneous Untrusted Data With Trusted Data through the improper handling of the x-nextjs-data header in middleware or proxy redirect responses. An attacker can disrupt access to redirect paths by injecting this header in requests, causing the middleware to generate a redirect response lacking a standard Location header. If a CDN or reverse proxy caches this malformed response without varying on the injected header, subsequent users may receive unusable redirects, resulting in service disruption until the cache is cleared.

Workaround

This vulnerability can be mitigated by configuring the CDN or reverse proxy to vary its cache key on x-nextjs-data for affected responses.

Remediation

Upgrade next to version 15.5.16, 16.2.5 or higher.

References

• GitHub Release
• GitHub Release
• Maintainer's Advisory

Overview

next is a react framework.

Affected versions of this package are vulnerable to Allocation of Resources Without Limits or Throttling via the handleAction Server Actions path in the App Router Edge runtime. An attacker can exhaust server memory by sending an oversized Server Action request, especially a multipart form submission, because the Edge handler reads the full body without enforcing serverActions.bodySizeLimit. This can crash or destabilize affected deployments and prevent legitimate Server Action requests from being processed.

Notes

• Affected deployments need App Router pages with at least one Server Action running in the Edge runtime; the issue is in that execution path rather than in Server Actions generally.
• The advisory’s practical ceiling is tied to hosting-side request body limits: if the platform does not cap uploads, an oversized multipart action request can still drive memory growth before application code sees it.

Workarounds

• Limit Server Actions request bodies at your hosting provider to 5 MiB maximum, so oversized multipart submissions cannot reach the Edge runtime and trigger excessive memory use.

Remediation

Upgrade next to version 15.5.21, 16.2.11 or higher.

References

• GitHub Commit
• GitHub Commit
• Maintainer's Advisory

Overview

next is a react framework.

Affected versions of this package are vulnerable to HTTP Request Smuggling during the rewrite of the proxy traffic to an external backend. An attacker can access unintended backend routes by sending crafted DELETE or OPTIONS requests with Transfer-Encoding: chunked headers. This is only exploitable if the application is not hosted on providers that handle rewrites at the CDN level.

Workaround

This vulnerability can be mitigated by blocking chunked DELETE/OPTIONS requests on rewritten routes at the edge/proxy, or by enforcing authentication and authorization on backend routes.

Remediation

Upgrade next to version 15.5.13, 16.1.7, 16.2.0-canary.102 or higher.

References

• GitHub Commit
• GitHub Commit
• GitHub Release
• GitHub Release

Overview

next is a react framework.

Affected versions of this package are vulnerable to Improper Encoding or Escaping of Output via the IncrementalCache.generateCacheKey function in next/dist/server/lib/incremental-cache. An attacker can make a server-side fetch return a cached response body from a different request by sending POST requests to the same URL with different non-UTF-8 request bodies that collapse to the same cache key. The affected cache key generation decodes request bodies as strings, so distinct byte sequences with invalid UTF-8 can hash to the same entry even though the requests are not deduped. This can leak confidential response data from one POST to an unauthorized request that uses a colliding body, breaking response isolation for server-side cached fetches.

Notes

• Applications using Pages Router are not affected; the advisory’s cache-key confusion is in the server-side fetch cache path used by the App Router/IncrementalCache flow.
• The issue is only reachable when request bodies are sent with a non-UTF-8 charset or otherwise contain byte sequences that do not round-trip as UTF-8; default UTF-8 request bodies do not trigger the collision described in the advisory.

Remediation

Upgrade next to version 15.5.21, 16.2.11 or higher.

References

• GitHub Advisory
• GitHub Commit
• GitHub PR

Overview

next is a react framework.

Affected versions of this package are vulnerable to Insertion of Sensitive Information Into Sent Data in action-handler.ts and action-utils.ts. An attacker can enumerate internal Server Action IDs by sending crafted Next-Action requests or probing client-served artifacts that reference those IDs. This exposes the presence of internal server functions and enables endpoint discovery on apps that use Server Actions, increasing the risk of further abuse when combined with other weaknesses.

Notes

• Publicly served client artifacts can reveal the full Server Action ID format, so the disclosure is not limited to active probing with Next-Action; attackers can also recover candidate IDs from browser-delivered chunks and manifests in apps that ship Server Actions.
• The advisory also covers use cache endpoints exposed through the same App Router server-function machinery, not just use server actions.

Workarounds

• Never assume authentication at the use cache or use server boundary; authenticate inside the Server Action or cache boundary itself so unauthenticated users cannot reach the internal endpoint.

Remediation

Upgrade next to version 15.5.21, 16.2.11 or higher.

References

• GitHub Commit
• GitHub Commit
• Maintainer's Advisory

Overview

next is a react framework.

Affected versions of this package are vulnerable to Interpretation Conflict via improper handling of shared cache entries for React Server Component responses. An attacker can cause unintended component payloads to be served to other users by manipulating shared cache behavior through crafted requests.

Workaround

This vulnerability can be mitigated by ensuring your CDN or reverse proxy keys on the relevant RSC request headers honor Vary, or by disabling shared caching for affected App Router and RSC responses.

Remediation

Upgrade next to version 15.5.16, 16.2.5 or higher.

References

• GitHub Release
• GitHub Release
• Maintainer's Advisory

Overview

next is a react framework.

Affected versions of this package are vulnerable to Use of Weak Hash via collisions in the _rsc cache-busting process. An attacker can manipulate cache entries by crafting requests that cause shared caches to serve incorrect response variants to users. This is only exploitable if deployments rely on shared caches with insufficient response partitioning.

Workaround

This vulnerability can be mitigated by ensuring intermediary caches correctly honor Vary for RSC-related request headers, or by disabling shared caching for affected RSC responses until a patched release is deployed.

Remediation

Upgrade next to version 15.5.16, 16.2.5 or higher.

References

• GitHub Release
• GitHub Release
• Maintainer's Advisory

Overview

next is a react framework.

Affected versions of this package are vulnerable to Use of Cache Containing Sensitive Information in createPatchedFetcher in packages/next/src/server/lib/patch-fetch.ts. An attacker can leak a cached response body from one request to another by sending server-side fetch(new Request(...), init) calls to the same URL with different request bodies or overrides. When the Request object and the separate init object diverge, the fetch cache can key the request differently from the effective upstream request, so a response generated for one body is reused for a different body. This exposes confidential data in cached POST responses to unauthorized requests.

Notes

• Applications using the Pages Router are not in scope for this issue; the advisory applies to the server-side patched fetch path.
• The leak requires fetch(new Request(...), init) where the separate init overrides the base Request; fetch(new Request(init), init) is the safe shape called out by the maintainers.

Remediation

Upgrade next to version 15.5.21, 16.2.11 or higher.

References

• GitHub Commit
• GitHub Commit
• Maintainer's Advisory

Overview

postcss is a PostCSS is a tool for transforming styles with JS plugins.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) in CSS Stringify Output. An attacker can execute arbitrary JavaScript code in the context of the affected web page by submitting crafted CSS containing </style> sequences that are not properly escaped when embedded within HTML <style> tags.

PoC

const postcss = require('postcss');

// Parse user CSS and re-stringify for page embedding
const userCSS = 'body { content: "</style><script>alert(1)</script><style>"; }';
const ast = postcss.parse(userCSS);
const output = ast.toResult().css;
const html = `<style>${output}</style>`;

console.log(html);
// <style>body { content: "</style><script>alert(1)</script><style>"; }</style>
//
// Browser: </style> closes the style tag, <script> executes

Details

Cross-site scripting (or XSS) is a code vulnerability that occurs when an attacker “injects” a malicious script into an otherwise trusted website. The injected script gets downloaded and executed by the end user’s browser when the user interacts with the compromised website.

This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.

Injecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.

Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, < can be coded as &lt; and > can be coded as &gt; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses < and > as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.

The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.

Types of attacks

There are a few methods by which XSS can be manipulated:

Affected environments

The following environments are susceptible to an XSS attack:

• Web servers
• Application servers
• Web application environments

How to prevent

This section describes the top best practices designed to specifically protect your code:

• Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
• Convert special characters such as ?, &, /, <, > and spaces to their respective HTML or URL encoded equivalents.
• Give users the option to disable client-side scripts.
• Redirect invalid requests.
• Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
• Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
• Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.

Remediation

Upgrade postcss to version 8.5.10 or higher.

References

• GitHub Advisory
• GitHub Commit
• GitHub Release

Overview

next is a react framework.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) in the beforeInteractive process, when untrusted input is embedded without proper escaping. An attacker can execute arbitrary JavaScript in a user's browser by injecting malicious content into the serialized script.

Workaround

This vulnerability can be mitigated by not passing untrusted data into beforeInteractive scripts, or by sanitizing or escaping the content before embedding it.

Details

Cross-site scripting (or XSS) is a code vulnerability that occurs when an attacker “injects” a malicious script into an otherwise trusted website. The injected script gets downloaded and executed by the end user’s browser when the user interacts with the compromised website.

This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.

Injecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.

Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, < can be coded as &lt; and > can be coded as &gt; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses < and > as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.

The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.

Types of attacks

There are a few methods by which XSS can be manipulated:

Affected environments

The following environments are susceptible to an XSS attack:

• Web servers
• Application servers
• Web application environments

How to prevent

This section describes the top best practices designed to specifically protect your code:

• Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
• Convert special characters such as ?, &, /, <, > and spaces to their respective HTML or URL encoded equivalents.
• Give users the option to disable client-side scripts.
• Redirect invalid requests.
• Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
• Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
• Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.

Remediation

Upgrade next to version 15.5.16, 16.2.5 or higher.

References

• GitHub Release
• GitHub Release
• Maintainer's Advisory

MPL-2.0 license