Incident Report: Swisscom domains temporary not reachable

Incident Notification to Partners

Subject: Incident Report: DDoS Attack Impacting DNS Services – Swisscom Incident #INC000013686431

Date: July 30, 2025

To: Signing Application Partners of Swisscom Trust Services

Management Summary:

On July 29, 2025, many partner using specific external DNS service provider for resolving Swisscom domains experienced service disruptions due to a DDoS attack targeting this external DNS service. Immediate measures were taken to adjust DNS settings, restoring service functionality.

Root Cause: The incident was traced to a DDoS attack one specific external DNS service.
This service in use in the data center configuration caused widespread service access issues.

Remedial Actions: DNS settings were corrected at 11:04 AM on July 29, 2025, changing the primary DNS configuration to ensure uninterrupted service. Until final propagation by all partners and cache updates the incident lasted measurable until 12:11 AM CEST.

Impact:

• Services Affected: DNS - Many Swisscom domains not being reachable during the incident.
  This included all Swisscom Trust Service domains.

Timeline of Key Events (CEST):

1. 7:28 AM - Initial Call: Investigations commenced. No immediate DNS issues detected, DDoS mitigation in progress.
2. 8:45 AM - Continued Troubleshooting: Persistent issue noticed, targeted testing performed, revealing errors accessing Swisscom sites.
   Primary DNS Reset: Tests indicated failed access through specific DNS, alternate DNS configurations applied.
3. 11:04 AM - DNS Update: Successful modification of DNS configurations restored site access, iterative authentication tests passed.

Resolution and Follow-up: The DNS change marked a significant improvement, with access restored and further tests confirming effectiveness.

Next Steps: A Problem Management Review will be conducted to address outstanding issues.

Conclusion: The incident has been resolved with no additional disturbances, and continuous monitoring is in place.

We value our partnership and are committed to preventing similar occurrences in the future. 

Best Regards,

Swisscom Trust Services