Threat actors have been exploiting CVE-2023-4966 in Citrix NetScaler ADC/Gateway devices since August

Experts reported that the vulnerability CVE-2023-4966 in Citrix NetScaler ADC/Gateway devices has been exploited in attacks since late August.

On October 10, Citrix published a security bulletin related to a critical vulnerability, tracked as CVE-2023-4966, in Citrix NetScaler ADC/Gateway devices.

“Exploits of CVE-2023-4966 on unmitigated appliances have been observed.” reported Citrix. “Cloud Software Group strongly urges customers of NetScaler ADC and NetScaler Gateway to install the relevant updated versions of NetScaler ADC and NetScaler Gateway as soon as possible: 

• NetScaler ADC and NetScaler Gateway 14.1-8.50  and later releases
• NetScaler ADC and NetScaler Gateway  13.1-49.15  and later releases of 13.1
• NetScaler ADC and NetScaler Gateway 13.0-92.19 and later releases of 13.0  
• NetScaler ADC 13.1-FIPS 13.1-37.164 and later releases of 13.1-FIPS  
• NetScaler ADC 12.1-FIPS 12.1-55.300 and later releases of 12.1-FIPS  
• NetScaler ADC 12.1-NDcPP 12.1-55.300 and later releases of 12.1-NDcPP 

Note: NetScaler ADC and NetScaler Gateway version 12.1 is now End-of-Life (EOL). Customers are recommended to upgrade their appliances to one of the supported versions that address the vulnerabilities.”

Researchers from Mandiant observed the exploitation of this vulnerability as a zero-day since late August.

Threat actors exploited this vulnerability to hijack existing authenticated sessions and bypass multifactor authentication or other strong authentication requirements. The researchers warn that these sessions may persist after the update to mitigate CVE-2023-4966 has been deployed. 

Mandiant also observed threat actors hijacking sessions where session data was stolen prior to the patch deployment and subsequently used by the threat actor. 

“The authenticated session hijacking could then result in further downstream access based upon the permissions and scope of access that the identity or session was permitted. A threat actor could utilize this method to harvest additional credentials, laterally pivot, and gain access to additional resources within an environment.” states Mandiant.

The attacks observed by Mandiant aimed at professional services, technology, and government organizations. 

The security firm published the CVE-2023-4966 guidance document for remediating and reducing risks related to this flaw.

At the end of July, Citrix warned customers that another flaw, tracked as CVE-2023-3519, in NetScaler Application Delivery Controller (ADC) and Gateway was being actively exploited in the wild.

IBM’s X-Force researchers recently reported that threat actors are conducting a large-scale credential harvesting campaign exploiting the recent CVE-2023-3519 vulnerability (CVSS score: 9.8) in Citrix NetScaler Gateways.

The vulnerability is a code injection that could result in unauthenticated remote code execution. The company added that successful exploitation requires that the appliance is configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) OR AAA virtual server.

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Pierluigi Paganini

(SecurityAffairs – hacking, Citrix)