On Tuesday 19 September 2023 at 17:32 UTC, a ACK flood targeted a news publisher customer in the Nordics. The attack peaked at 261.3 Gbps and lasted 33 minutes. Traffic originated from 2275 autonomous systems in 14 countries, predominantly compromised cloud VMs.
| Vector | ACK flood |
| Peak | 261.3 Gbps |
| Duration | 33 min |
| Time to mitigation | 0.477 s |
| Attack traffic reaching origin | 0.042% |
| Legitimate traffic challenged | 0.62% |
Timeline
The attack was preceded by no stated motive. Edge packet filters identified the flood by source port and payload signature and dropped it at line rate across 28 points of presence.
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.
- Lower challenge thresholds on authentication endpoints during high-risk events.
- Enable log streaming to your SIEM for faster correlation.
Solid runbook advice. The DNS-at-2am point hit home.
We moved from a scrubbing provider to always-on last year; time to mitigation went from minutes to basically nothing.
Verified good bots and allow-listed partners bypass challenges entirely.