On Wednesday 21 May 2025 at 16:36 UTC, a Slowloris targeted a online payments customer in the UK. The attack peaked at 420.6 million requests per second and lasted 15 minutes. Traffic originated from 756 autonomous systems in 19 countries, predominantly mobile carrier ranges.
| Vector | Slowloris |
| Peak | 420.6 million requests per second |
| Duration | 15 min |
| Time to mitigation | 0.774 s |
| Attack traffic reaching origin | 0.040% |
| Legitimate traffic challenged | 0.44% |
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 157 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
Checkout conversion was unchanged compared with the same hour of the previous week.
Recommendations
- Lower challenge thresholds on authentication endpoints during high-risk events.
- Add a dedicated rate limit for the targeted route.
- Review allow-listed partner ranges quarterly.
Any plans to support per-tenant limits keyed on a JWT claim?