DDoS attacks are increasing in scale and complexity, threatening to overwhelm the internal resources of businesses around the world. The F5 Silverline Security Operations Center (SOC) recently saw a new distributed denial-of-service (DDoS) attack vector targeting a customer’s DNS servers with malicious traffic averaging between 8 and 12 Mbps and bursts of malicious traffic peaking at over 100 Mbps. This attack began in mid-August and continued through November 2015. It was not a typical reflection attack where DNS servers are used to attack a web site, but an attack against the actual DNS servers. Through additional investigation, the SOC analysts identified the vector and crafted a targeted mitigation for this new “_dmarc” attack. 
In their investigation, Edgar Ojeda and his colleagues found that F5 Silverline customer's DNS servers were receiving hundreds of thousands of randomized queries for “_dmarc” DNS records even if from a volumetric standpoint this amount of traffic seems to be trivial. Then, they noticed that _dmarc DNS queries were for non-existent subdomains and that customer’s DNS infrastructure was becoming unstable. 
As the attack continued and after further investigation, F5 SOC created a finely tuned signature that successfully scrubbed all malicious traffic and the customer’s service became operational again.

To read the full report describing the attack, click here.

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