Threat Bulletin 1367: UDP reflection (DNS) against a healthcare portal platform in the Nordics

On Wednesday 20 May 2026 at 19:44 UTC, a UDP reflection (DNS) targeted a healthcare portal customer in the Nordics. The attack peaked at 241.1 Gbps and lasted 144 minutes. Traffic originated from 91 autonomous systems in 59 countries, predominantly misconfigured open reflectors.

Vector UDP reflection (DNS)
Peak 241.1 Gbps
Duration 144 min
Time to mitigation 0.246 s
Attack traffic reaching origin 0.031%
Legitimate traffic challenged 0.33%

Timeline

The attack was preceded by a hacktivist channel announcing the target. Edge packet filters identified the flood by source port and payload signature and dropped it at line rate across 40 points of presence.

What the customer saw

The customer’s status page stayed green throughout; they learned about the attack from our notification.

Recommendations

  • Add a dedicated rate limit for the targeted route.
  • Keep origin IPs out of public DNS history.
  • Lower challenge thresholds on authentication endpoints during high-risk events.

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