On Tuesday 30 November 2021 at 20:19 UTC, a HTTP/2 rapid reset targeted a online payments customer in the UK. The attack peaked at 653.3 million requests per second and lasted 79 minutes. Traffic originated from 3956 autonomous systems in 65 countries, predominantly a rented booter service.
| Vector | HTTP/2 rapid reset |
| Peak | 653.3 million requests per second |
| Duration | 79 min |
| Time to mitigation | 0.161 s |
| Attack traffic reaching origin | 0.010% |
| Legitimate traffic challenged | 0.69% |
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 755 within 8 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
- Keep origin IPs out of public DNS history.
- Lower challenge thresholds on authentication endpoints during high-risk events.
- Enable authenticated origin pulls.
How do you avoid challenging uptime monitors and partners?
Good question. We will cover that in a follow-up post.