VERY IMPORTANT

Since January 10, 2020, FireEye has tracked extensive global exploitation of CVE-2019-19781, which continues to impact Citrix ADC and Gateway instances that are unpatched or do not have mitigations applied. We previously reported on attackers’ swift attempts to exploit this vulnerability and the post-compromise deployment of the previously unseen NOTROBIN malware family by one threat actor. FireEye continues to actively track multiple clusters of activity associated with exploitation of this vulnerability, primarily based on how attackers interact with vulnerable Citrix ADC and Gateway instances after identification.