On Thursday 4 March 2021 at 03:22 UTC, a Slowloris targeted a healthcare portal customer in Iberia. The attack peaked at 643.3 million requests per second and lasted 62 minutes. Traffic originated from 1159 autonomous systems in 60 countries, predominantly misconfigured open reflectors.
| Vector | Slowloris |
| Peak | 643.3 million requests per second |
| Duration | 62 min |
| Time to mitigation | 0.603 s |
| Attack traffic reaching origin | 0.059% |
| Legitimate traffic challenged | 0.04% |
Timeline
The attack was preceded by a publicly announced sales event. Request rates on the targeted routes exceeded their hourly baseline by a factor of 287 within 13 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
- Add a dedicated rate limit for the targeted route.
- Lower challenge thresholds on authentication endpoints during high-risk events.
- Review allow-listed partner ranges quarterly.
We moved from a scrubbing provider to always-on last year; time to mitigation went from minutes to basically nothing.
This matches what we see in iGaming around big matches.
How do you avoid challenging uptime monitors and partners?
Could you share the dataset behind the percentages?
Interesting that most attacks are under ten minutes. Our experience is similar.
Nice to read a vendor blog that admits what went wrong.