On Thursday 29 April 2021 at 23:02 UTC, a Slowloris targeted a municipal services customer in Iberia. The attack peaked at 645.3 million requests per second and lasted 116 minutes. Traffic originated from 4099 autonomous systems in 97 countries, predominantly a Mirai-derived IoT botnet.
| Vector | Slowloris |
| Peak | 645.3 million requests per second |
| Duration | 116 min |
| Time to mitigation | 0.213 s |
| Attack traffic reaching origin | 0.034% |
| Legitimate traffic challenged | 0.21% |
Timeline
The attack was preceded by a breaking political story. Request rates on the targeted routes exceeded their hourly baseline by a factor of 873 within 6 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 122 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.
Nice to read a vendor blog that admits what went wrong.
We moved from a scrubbing provider to always-on last year; time to mitigation went from minutes to basically nothing.
Interesting that most attacks are under ten minutes. Our experience is similar.
Solid runbook advice. The DNS-at-2am point hit home.