Microsoft: Azure DDoS attack amplified by cyber-defense error

Microsoft blamed an implementation error for amplifying the impact of a distributed denial-of-service (DDoS) attack yesterday, which ended up disrupting the company’s Azure cloud services for nearly eight hours.

The attack affected several Azure offerings, including Azure App Services, Azure IoT Central, Application Insights, Log Search Alerts, and Azure Policy. The disruption, which began at around 7:45 a.m. ET and lasted until 3:43 p.m. ET, also impacted the main Azure portal and a subset of Microsoft 365 and Microsoft Purview data-protection services.

DDoS Cyber-Defense Error Under Investigation

In an event summary yesterday, Microsoft described the DDoS attack as causing an “unexpected usage spike [that] resulted in Azure Front Door (AFD) and Azure Content Delivery Network (CDN) components performing below acceptable thresholds.” The spike caused intermittent service errors, timeouts, and sudden latency increases.

More concerningly in some ways, “while the initial trigger event was a DDoS attack, which activated our DDoS protection mechanisms, initial investigations suggest that an error in the implementation of our defenses amplified the impact of the attack rather than mitigating it.”

Microsoft has not specifically identified the mistake that exacerbated the DDoS attack. But according to its description of the events of July 30, the initial network configuration changes the company made to support DDoS mitigation efforts may have led to some unexpected “side effects.” The company implemented an updated approach that it first rolled out in thbe Asia-Pacific region and Europe, and then deployed in the Americas after validating the approach worked.

“Our team will be completing an internal retrospective to understand the incident in more detail,” Microsoft said. “We will publish a Preliminary Post Incident Review (PIR) within approximately 72 hours, to share more details on what happened and how we responded.”

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