Webhooks, Integrations & the SSRF Playground

Let's end on a juicy one: webhooks and server-side integrations. These features — where an app makes requests to other servers on your behalf — are basically an SSRF playground. If you understood the SSRF and cloud posts, this is where it all comes together.

What Are Webhooks & Integrations?

Modern apps constantly talk to OTHER servers:

• Webhooks: "when X happens, send a notification to THIS URL" — and often YOU get to specify the URL
• Integrations: connect your account to Slack, Zapier, payment providers, etc.
• URL-fetch features: "import from URL," link previews, PDF generators, avatar-from-URL
• Callbacks: OAuth flows, payment confirmations

See the common thread? In many of these, the app's SERVER makes a request to a URL — and sometimes YOU control that URL. And a server making requests to URLs you control is the definition of potential SSRF.

Why This Is An SSRF Playground

Webhooks are almost purpose-built for SSRF testing:

1. The feature literally asks you for a URL to send requests to
2. The server dutifully sends requests there
3. So you point it at INTERNAL targets instead of your server
4. Internal services, cloud metadata (169.254.169.254 — post 26!), localhost admin panels — all potentially reachable

It's SSRF with a friendly "please enter a URL" form.

How To Hunt It

1. Find any feature that sends server-side requests to a URL (webhook config, import-from-URL, link preview, integration callback)
2. First, point it at YOUR listener (Burp Collaborator) — confirm the server actually reaches out
3. Note details: what does the request look like? Does it follow redirects? What can it reach?
4. Now aim internal: 127.0.0.1, localhost, internal IP ranges, cloud metadata
5. Try bypasses when blocked (alternate IP formats, redirects, DNS tricks — post 5)
6. Escalate toward impact: internal services, metadata credentials, port scanning the internal network

Beyond SSRF: Other Webhook Bugs

Webhooks and integrations hide other bugs too:

• Data leakage: does the webhook payload contain sensitive data you can capture?
• Injection into the integration: can you inject content that executes in the connected service (like Slack/Discord formatting or command injection)?
• Auth issues: can you register a webhook for data you shouldn't receive? Point another user's notifications to YOUR endpoint?
• Signature bypass: if webhooks are "signed" for security, is the signature actually verified?

That's our Series 2 — Congrats!

You made it through 30 more posts — real hunt stories, AI hacking, recon mastery, and cloud/API security. Combined with batch 1, you've got a genuinely serious bug bounty library now. Go put it to work. And remember: always authorized, always ethical. We hack for good. 🛡️❤️

— Nitin

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