On Sunday 23 February 2025 at 09:04 UTC, a HTTP/2 rapid reset targeted a tax authority portal customer in the Nordics. The attack peaked at 929.3 million requests per second and lasted 26 minutes. Traffic originated from 2021 autonomous systems in 54 countries, predominantly compromised cloud VMs.
| Vector | HTTP/2 rapid reset |
| Peak | 929.3 million requests per second |
| Duration | 26 min |
| Time to mitigation | 0.487 s |
| Attack traffic reaching origin | 0.027% |
| Legitimate traffic challenged | 0.10% |
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 570 within 29 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
Checkout conversion was unchanged compared with the same hour of the previous week.
Recommendations
- Enable authenticated origin pulls.
- Lower challenge thresholds on authentication endpoints during high-risk events.
- Enable log streaming to your SIEM for faster correlation.
Our auditors asked for exactly this kind of incident evidence under DORA.
Interesting that most attacks are under ten minutes. Our experience is similar.
Great to hear, thanks for sharing your experience.