On Saturday 14 August 2021 at 15:45 UTC, a TLS handshake exhaustion targeted a municipal services customer in North America. The attack peaked at 186.6 million requests per second and lasted 170 minutes. Traffic originated from 3607 autonomous systems in 37 countries, predominantly compromised cloud VMs.
| Vector | TLS handshake exhaustion |
| Peak | 186.6 million requests per second |
| Duration | 170 min |
| Time to mitigation | 0.556 s |
| Attack traffic reaching origin | 0.067% |
| Legitimate traffic challenged | 0.09% |
Timeline
The attack was preceded by a breaking political story. Request rates on the targeted routes exceeded their hourly baseline by a factor of 816 within 16 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
- Enable log streaming to your SIEM for faster correlation.
- Lower challenge thresholds on authentication endpoints during high-risk events.
- Review allow-listed partner ranges quarterly.