Anatomy of a Security Incident: Our Postmortem
Complete transparency about a breach attempt we thwarted. How our security layers worked, what we learned, and changes we made.
On January 15th at 2:47 AM, our intrusion detection system flagged unusual API activity. What followed was a 36-hour incident response that tested every layer of our security infrastructure. Here's what happened, how we responded, and what we changed.
The attack began with credential stuffing—automated login attempts using credentials leaked from other services. This isn't uncommon; we see thousands of these attempts daily. Our rate limiting and CAPTCHA systems blocked 99.9% of them. But 0.1% got through due to a bug in our rate limiting logic when requests came through our CDN.
Once inside, the attacker attempted lateral movement. They discovered an internal API endpoint that wasn't properly authenticated—a legacy endpoint from a feature we'd deprecated but never removed. This allowed enumeration of user data. However, our data access logging caught the anomaly: a single account accessing 10,000 user profiles in 10 minutes.
Our response was immediate. We locked the compromised account, revoked all sessions, and deployed a hotfix to secure the exposed endpoint within 20 minutes of detection. We enabled enhanced logging across all services and began forensic analysis.
The post-incident review was thorough. We discovered the endpoint vulnerability during a code review three months prior but incorrectly triaged it as low priority because we thought it was unused. We found similar deprecated endpoints in two other services.
Changes implemented: automatic security scanning in CI/CD that fails builds with any unauthenticated endpoints, quarterly security audits of all API routes, enhanced anomaly detection that triggers on unusual data access patterns, and improved rate limiting that works correctly regardless of request origin.
We also improved our incident response playbook, adding runbooks for common attack patterns and pre-staged response actions. Our mean time to detection dropped from 20 minutes to under 5 minutes in subsequent incidents.
Transparency is important to us. No user data was exfiltrated—we confirmed this through log analysis and network egress monitoring. But we reported the incident to affected users anyway and offered identity monitoring services. Security is a continuous process, not a destination.