The U.S. Cybersecurity and Infrastructure Security Agency (CISA) issued an advisory warning about a critical security flaw in Citrix NetScaler Application Delivery Controller (ADC) and Gateway devices. The vulnerability, tracked as CVE-2023-3519 with a CVSS score of 9.8, allows unauthenticated remote code execution.
Threat actors exploited this zero-day vulnerability in June 2023 to drop a web shell on a non-production environment NetScaler ADC appliance belonging to a critical infrastructure organization. The web shell provided the attackers with access to the victim’s active directory (AD) and allowed them to collect and exfiltrate AD data. However, network segmentation controls for the appliance prevented lateral movement to a domain controller.
Furthermore, the web shell deployed by the threat actors enabled the collection of sensitive information, including NetScaler configuration files, NetScaler decryption keys, and AD data. The attackers transmitted this data as a PNG image file named “medialogininit.png.” While they attempted to move laterally across the network and identify accessible targets, robust network segmentation practices blocked their efforts.
Additionally, the actors tried to delete their artifacts to cover their tracks. The specific organization impacted by this incident was not disclosed by CISA, and the identity of the threat actors and their country of origin remains unknown.
Vulnerabilities in gateway products like Citrix NetScaler ADC and Gateway have become attractive targets for threat actors seeking privileged access to targeted networks. To mitigate potential threats, CISA urges users to apply the latest patches promptly. By doing so, organizations can secure their systems against similar exploits and protect sensitive data from unauthorized access and exfiltration.
In summary, CISA’s advisory highlights the active exploitation of a critical vulnerability in Citrix NetScaler ADC and Gateway devices by threat actors who deployed web shells to access and collect sensitive data from a targeted critical infrastructure organization.
While robust network segmentation prevented further lateral movement, the incident underscores the importance of prompt updates and patching to protect against potential threats targeting gateway products.
