Earlier this week, Citrix alerted customers to three vulnerabilities in its NetScaler ADC and NetScaler Gateway products. Surfaced by researchers at Resillion, these vulnerabilities include a critical flaw currently being exploited in the wild to give attackers unauthenticated remote code execution on vulnerable NetScaler targets (CVE-2023-3519). Compromised organizations include a critical infrastructure entity in the U.S., where attackers gained access last month and successfully exfiltrated Active Directory data. And at the time of publication, there appear to be over 5,000 public-facing vulnerable NetScaler targets.
What are Citrix NetScaler ADCs and Gateways? #
NetScaler Application Delivery Controller (ADC), formerly known as Citrix ADC, acts in a number of capacities to ensure reliable application delivery to users. This can include load balancing across application servers, off-loading of certain operations, security protections, and policy enforcement.
NetScaler Gateway, formerly known as Citrix Gateway, provides single sign-on (SSO) from any device to multiple applications through a single URL.
What is the impact? #
The three reported vulnerabilities affecting NetScaler ADC and Gateway products are of various types, and each include different preconditions required for exploitation:
- Unauthenticated remote code execution (CVE-2023-3519; CVSS score 9.8 – “critical”)
- Successful exploitation requires the NetScaler target be configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, or RDP Proxy) or “authentication, authorization, and auditing” (AAA) virtual server.
- Reflected cross-site scripting (XSS) (CVE-2023-3466; CVSS score 8.3 – “high”)
- Successful exploitation requires the victim to be on the same network as the vulnerable NetScaler target when the victim loads a malicious link (planted by the attacker) in their web browser.
- Privilege escalation to root administrator (nsroot) (CVE-2023-3467; CVSS score 8.0 – “high”)
- Successful exploitation requires an attacker having achieved command-line access on a vulnerable NetScaler target.
U.S.-based CISA has reported attackers exploiting CVE-2023-3519 to install webshells used in further network exploration and data exfiltration, causing CVE-2023-3519 to be added to CISA’s Known Exploited Vulnerabilities Catalog. Other common attacker goals, like establishing persistence, lateral movement, and malware deployment, are potential outcomes following successful exploitation.
Are updates available? #
Citrix has made patched firmware updates available. Admins should update older firmware on vulnerable NetScaler devices as soon as possible.
CISA has also made additional information available around indicators of compromise and mitigations.
How do I find potentially vulnerable NetScaler instances with runZero? #
hw:netscaler or os:netscaler
Results from the above query should be triaged to verify they are affected ADC or Gateway products and if they are running updated firmware versions.
Results from the above query should be triaged to verify they are affected ADC or Gateway products and if they are updated versions.
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runZero, a network discovery and asset inventory solution, was founded in 2018 by HD Moore, the creator of Metasploit. HD envisioned a modern active discovery solution that could find and identify everything on a network–without credentials. As a security researcher and penetration tester, he often employed benign ways to get information leaks and piece them together to build device profiles. Eventually, this work led him to leverage applied research and the discovery techniques developed for security and penetration testing to create runZero.