On Wednesday 28 July 2021 at 03:14 UTC, a Slowloris targeted a B2B SaaS customer in the UK. The attack peaked at 950.7 million requests per second and lasted 166 minutes. Traffic originated from 1934 autonomous systems in 113 countries, predominantly a rented booter service.
| Vector | Slowloris |
| Peak | 950.7 million requests per second |
| Duration | 166 min |
| Time to mitigation | 0.624 s |
| Attack traffic reaching origin | 0.006% |
| 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 450 within 23 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 116 ms during the first minute, then normal service.
Recommendations
- Enable authenticated origin pulls.
- Add a dedicated rate limit for the targeted route.
- Review allow-listed partner ranges quarterly.
Do you publish the edge IP ranges in a machine-readable format?
Interesting that most attacks are under ten minutes. Our experience is similar.