The Cybersecurity and Infrastructure Security Agency (CISA) has released an update to a previously published Cybersecurity Advisory (CSA), Threat Actors Exploiting Citrix CVE-2023-3519 to Implant Webshells. The CSA—originally released to warn network defenders of critical infrastructure organizations about threat actors exploiting CVE-2023-3519, an unauthenticated remote code execution (RCE) vulnerability affecting NetScaler (formerly Citrix) Application Delivery Controller (ADC) and NetScaler Gateway—contains victim information gathered in August 2023. Since July 2023, the Joint Cyber Defense Collaborative (JCDC) has facilitated continuous, real-time threat information sharing with and between partners on post-exploitation activity of CVE-2023-3519. JCDC consolidated and shared detection methods, threat actor tactics, techniques, and procedures (TTPs), and indicators of compromise (IOCs) received from industry and international partners. The updated CSA contains new TTPs as well as IOCs received from some of these partners and an additional victim.
CISA strongly urges all critical infrastructure organizations to review the advisory and follow the mitigation recommendations—such as prioritizing patching known exploited vulnerabilities like Citrix CVE-2023-3519.