On Monday 17 May 2021 at 02:11 UTC, a Slowloris targeted a online casino customer in North America. The attack peaked at 298.1 million requests per second and lasted 141 minutes. Traffic originated from 2215 autonomous systems in 31 countries, predominantly misconfigured open reflectors.
| Vector | Slowloris |
| Peak | 298.1 million requests per second |
| Duration | 141 min |
| Time to mitigation | 0.257 s |
| Attack traffic reaching origin | 0.010% |
| Legitimate traffic challenged | 0.51% |
Timeline
The attack was preceded by an extortion email received two days earlier. Request rates on the targeted routes exceeded their hourly baseline by a factor of 626 within 16 seconds. The risk score of participating clients crossed the challenge threshold automatically and proof-of-work difficulty rose with origin load.
What the customer saw
No customer-visible impact. The on-call engineer was notified and acknowledged the incident from the dashboard.
Recommendations
- Lower challenge thresholds on authentication endpoints during high-risk events.
- Add a dedicated rate limit for the targeted route.
- Keep origin IPs out of public DNS history.