Abusing Webhooks: The Silent Data Exfiltration and Command & Control Channel

In modern cloud-native architectures and SaaS ecosystems, webhooks are indispensable. They enable real-time automation, third-party integrations, and cross-platform orchestration.

But what if I told you that webhooks - those harmless HTTP callbacks, can be weaponized into stealthy data exfiltration channels and even act as a form of command and control (C2)?

This post breaks down how malicious actors abuse webhooks, explores a real-world scenario, and gives defenders practical detection and mitigation strategies. Whether you're blue team, red team, or cloud architect, this is knowledge you need to integrate into your threat model.

What Are Webhooks?

A webhook is a user-defined HTTP callback, triggered by an event. Instead of polling for updates, applications can “push” data to a specified URL in real-time.

Common Use Cases:

• GitHub → Slack notifications on push

• Stripe → Payment status updates

• Jira → Auto-create incidents in PagerDuty

They typically use a POST request with JSON or form-encoded payloads to an external URL.

How Attackers Abuse Webhooks?

Objective:

• Exfiltrate sensitive data (credentials, logs, PII)

• Maintain persistence or covertly receive commands

• Avoid triggering traditional security tools (EDR, DLP, IDS)

Techniques:

• Webhook Misconfiguration Exploitation

  • Attackers identify exposed webhook URLs and:

    • Replace the target URL with their server

    • Inject malicious scripts into webhook payloads

    • Abuse webhook events to trigger unauthorized workflows

• Data Exfiltration via Legitimate Webhooks

  • Create a new webhook (e.g., in GitHub, Slack, Jira, or Confluence)

  • Set the payload URL to their attacker-controlled listener

  • Configure it to trigger on sensitive events (e.g., code pushes, issue creation)

  • Receive internal data in real time over a standard HTTPS channel

Webhook traffic often looks like normal SaaS API traffic, bypassing most firewalls, EDRs.

Abusing Webhook

Real-World Case Study: GitHub & Slack Webhook Exfiltration

In 2023, a targeted attack on a fintech company involved a compromised GitHub repo and unauthorized webhook creation.

• Attacker gained limited access to a developer’s GitHub token via phishing.

• Created a new webhook on a repository used for deployment automation.

• The webhook sent every new commit (including .env secrets and credentials) to https://attacker-c2[.]com/webhook.

• Slack integrations were also modified to send sensitive alerts to attacker channels.

Credentials to production DB and AWS were compromised; over 6 TB of data accessed.

Mitigation Strategies

Governance Controls:

• Implement scoped API tokens with least privilege

• Use domain allowlisting for webhook destinations

• Enforce approval workflows for webhook creation

Token Hygiene:

• Periodically rotate and audit API tokens

• Revoke unused tokens via GitHub or Slack management console

Webhook abuse is a low-noise, high-impact vector that fits perfectly into modern cloud attack chains. As organizations increasingly rely on SaaS, the security of the integrations themselves becomes the new perimeter.

"In a world of APIs and automations, the weakest link isn’t malware, it’s misconfiguration."

Note: Feel free to drop your thoughts in the comments below - whether it's feedback, a topic you'd love to see covered, or just to say hi! Don't forget to join the forum for more engaging discussions and stay updated with the latest blog posts. Let's keep the conversation going and make cybersecurity a community effort!

-AJ