On Friday 16 February 2024 at 23:16 UTC, a HTTP/2 rapid reset targeted a tax authority portal customer in the Nordics. The attack peaked at 724.0 million requests per second and lasted 88 minutes. Traffic originated from 2118 autonomous systems in 100 countries, predominantly a headless-browser farm.
| Vector | HTTP/2 rapid reset |
| Peak | 724.0 million requests per second |
| Duration | 88 min |
| Time to mitigation | 0.784 s |
| Attack traffic reaching origin | 0.004% |
| Legitimate traffic challenged | 0.10% |
Timeline
The attack was preceded by a hacktivist channel announcing the target. Request rates on the targeted routes exceeded their hourly baseline by a factor of 180 within 28 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
A brief increase in p99 latency of 169 ms during the first minute, then normal service.
Recommendations
- Enable log streaming to your SIEM for faster correlation.
- Lower challenge thresholds on authentication endpoints during high-risk events.
- Keep origin IPs out of public DNS history.