Hynes/Void-Homelab
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fix(ingest): pin resolved IP into safe_fetch to defeat DNS-rebinding

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Replaces the validate-then-call-fetch pattern (which left a TOCTOU
window where the OS resolver could return a different IP at connect
time) with an undici Agent dispatcher whose lookup() returns the IP we
already validated. Same hardening on every redirect hop.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
This commit is contained in:
root
2026-06-01 03:48:52 +10:00
parent e558be49a9
commit 99ab1ffb70
1 changed files with 25 additions and 8 deletions
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33
lib/ingest/safe_fetch.js
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@@ -1,16 +1,17 @@
// Wraps fetch with SSRF mitigations:
// - http/https only
// - DNS-resolve host and reject loopback/RFC1918/link-local/CGNAT/zero
// - Pin the resolved IP into the request so a rebind between resolve and
// connect cannot redirect to an internal address
// - Follow redirects manually with the same validation on each hop
// - Pin the resolved IP into the undici dispatcher so a rebind between
// our validation lookup and the TCP connect cannot point us at an
// internal address (TOCTOU defeat).
// - Follow redirects manually with the same validation on each hop.
//
// Defaults can be loosened via VOID_INGEST_ALLOW_PRIVATE=true (for dev/test
// against fixtures that hit 127.0.0.1).
// Defaults can be loosened via VOID_INGEST_ALLOW_PRIVATE=true for tests
// that hit 127.0.0.1 fixtures.
import { lookup } from 'node:dns/promises';
import net from 'node:net';
import { Agent } from 'node:https';
import { Agent } from 'undici';
const BLOCK_V4 = [
['0.0.0.0', 8],
@@ -64,6 +65,16 @@ async function resolveAndCheck(host) {
return records[0];
}
function pinnedDispatcher(address, family) {
return new Agent({
connect: {
// undici will call our lookup instead of OS DNS, so the chosen IP
// is the one we already validated. No TOCTOU re-resolution.
lookup: (_hostname, _options, cb) => cb(null, address, family)
}
});
}
export async function safeFetch(url, options = {}, { maxHops = 5 } = {}) {
let current = url;
for (let hop = 0; hop <= maxHops; hop++) {
@@ -71,12 +82,18 @@ export async function safeFetch(url, options = {}, { maxHops = 5 } = {}) {
if (u.protocol !== 'http:' && u.protocol !== 'https:') {
throw new SafeFetchError(`unsupported scheme ${u.protocol}`, 'scheme');
}
let address, family;
if (net.isIP(u.hostname)) {
if (isBlockedAddr(u.hostname)) throw new SafeFetchError(`blocked literal IP ${u.hostname}`, 'blocked_addr');
address = u.hostname;
family = net.isIPv4(u.hostname) ? 4 : 6;
} else {
await resolveAndCheck(u.hostname);
const rec = await resolveAndCheck(u.hostname);
address = rec.address;
family = rec.family;
}
const res = await fetch(current, { ...options, redirect: 'manual' });
const dispatcher = pinnedDispatcher(address, family);
const res = await fetch(current, { ...options, redirect: 'manual', dispatcher });
if ([301,302,303,307,308].includes(res.status)) {
const loc = res.headers.get('location');
if (!loc) throw new SafeFetchError('redirect without Location', 'bad_redirect');