On Friday 18 June 2021 at 22:37 UTC, a Slowloris targeted a news publisher customer in Iberia. The attack peaked at 922.4 million requests per second and lasted 84 minutes. Traffic originated from 4017 autonomous systems in 32 countries, predominantly a Mirai-derived IoT botnet.
| Vector | Slowloris |
| Peak | 922.4 million requests per second |
| Duration | 84 min |
| Time to mitigation | 0.351 s |
| Attack traffic reaching origin | 0.056% |
| Legitimate traffic challenged | 0.20% |
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 536 within 38 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
The customer’s status page stayed green throughout; they learned about the attack from our notification.
Recommendations
- Add a dedicated rate limit for the targeted route.
- Lower challenge thresholds on authentication endpoints during high-risk events.
- Keep origin IPs out of public DNS history.
Solid runbook advice. The DNS-at-2am point hit home.
Machine-readable ranges are at /ips.json and via the API.