On Tuesday 11 May 2021 at 12:01 UTC, a UDP reflection (DNS) targeted a retail banking customer in Iberia. The attack peaked at 289.1 Gbps and lasted 32 minutes. Traffic originated from 3757 autonomous systems in 111 countries, predominantly a Mirai-derived IoT botnet.
| Vector | UDP reflection (DNS) |
| Peak | 289.1 Gbps |
| Duration | 32 min |
| Time to mitigation | 0.756 s |
| Attack traffic reaching origin | 0.027% |
| Legitimate traffic challenged | 0.63% |
Timeline
The attack was preceded by a publicly announced sales event. Edge packet filters identified the flood by source port and payload signature and dropped it at line rate across 39 points of presence.
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.
- Enable log streaming to your SIEM for faster correlation.
- Review allow-listed partner ranges quarterly.
Would love a follow-up on how you handle HTTP/3 fingerprinting.
Verified good bots and allow-listed partners bypass challenges entirely.
Any plans to support per-tenant limits keyed on a JWT claim?
Thanks — sharing this with our on-call team.
Thanks! Yes — the risk score and its components are included in every log record.
Solid runbook advice. The DNS-at-2am point hit home.
How do you avoid challenging uptime monitors and partners?
How do you avoid challenging uptime monitors and partners?