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Citrix has issued an emergency advisory warning its customers of a security issue affecting its NetScaler application delivery controller (ADC) devices that attackers are abusing to launch amplified distributed denial-of-service (DDoS) attacks against several targets.

“An attacker or bots can overwhelm the Citrix ADC [Datagram Transport Layer Security] network throughput, potentially leading to outbound bandwidth exhaustion,” the company noted. “The effect of this attack appears to be more prominent on connections with limited bandwidth.”

ADCs are purpose-built networking appliances whose function is to improve the performance, security, and availability of applications delivered over the web to end-users.

The desktop virtualization and networking service provider said it’s monitoring the incident and is continuing to investigate its impact on Citrix ADC, adding “the attack is limited to a small number of customers around the world.”

The issue came to light after multiple reports of a DDoS amplify attack over UDP/443 against Citrix (NetScaler) Gateway devices at least since December 19, according to Marco Hofmann, an IT administrator for a German software firm ANAXCO GmbH.

images from Hacker News