On Sunday 26 September 2021 at 03:41 UTC, a TLS handshake exhaustion targeted a online payments customer in North America. The attack peaked at 544.4 million requests per second and lasted 128 minutes. Traffic originated from 4073 autonomous systems in 91 countries, predominantly misconfigured open reflectors.
| Vector | TLS handshake exhaustion |
| Peak | 544.4 million requests per second |
| Duration | 128 min |
| Time to mitigation | 0.948 s |
| Attack traffic reaching origin | 0.018% |
| Legitimate traffic challenged | 0.56% |
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 351 within 9 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
No customer-visible impact. The on-call engineer was notified and acknowledged the incident from the dashboard.
Recommendations
- Enable authenticated origin pulls.
- Review allow-listed partner ranges quarterly.
- Enable log streaming to your SIEM for faster correlation.