Citrix Patches Critical Vulnerability in ADC Gateway [CVE-2021-22955 and CVE-2021-22956]

CVE numbers CVE-2021-22955 and CVE-2021-22956

Vulnerabilities have been discovered in Citrix ADC (formerly known as NetScaler ADC), Citrix Gateway (formerly known as NetScaler Gateway), and Citrix SD-WAN WANOP Edition models 4000-WO, 4100-WO, 5000-WO, and 5100-WO. 

These vulnerabilities, if exploited, could result in a Unauthenticated denial of service or Temporary disruption of the Management GUI, Nitro API and RPC communication.

CVE-2021-22955 

The following supported versions of Citrix ADC and Citrix Gateway are affected by this vulnerability: 

• Citrix ADC and Citrix Gateway 13.0 before 13.0-83.27 

• Citrix ADC and Citrix Gateway 12.1 before 12.1-63.22 
• Citrix ADC and NetScaler Gateway 11.1 before 11.1-65.23 
• Citrix ADC 12.1-FIPS before 12.1-55.257 

CVE-2021-22956

All supported versions of Citrix ADC, Citrix Gateway, and Citrix SD-WAN WANOP Edition are affected by this vulnerability until the appliance has been configured according to the Citrix Application Delivery Controller, Citrix Gateway, and Citrix SD-WAN WANOP Edition – Management Module Configuration Reference Guide. 

The following supported versions of Citrix ADC, Citrix Gateway, and Citrix SD-WAN WANOP Edition support this configuration change: 

• Citrix ADC and Citrix Gateway 13.1-4.43 and later releases 
• Citrix ADC and Citrix Gateway 13.0-83.27 and later releases of 13.0 
• Citrix ADC and Citrix Gateway 12.1-63.22 and later releases of 12.1 
• Citrix ADC and NetScaler Gateway 11.1-65.23 and later releases of 11.1 
• Citrix ADC 12.1-FIPS 12.1-55.257 and later releases of 12.1-FIPS  
• Citrix SD-WAN WANOP Edition 11.4.2 and later releases of 11.4 
• Citrix SD-WAN WANOP Edition 10.2.9c and later releases of 10.2 

Please note that the WANOP feature of SD-WAN Premium Edition is not impacted. 

This bulletin only applies to customer-managed Citrix ADC, Citrix Gateway and Citrix SD-WAN WANOP Edition appliances. Customers using Citrix-managed cloud services do not need to take any action. 

Mitigating Factors

CVE-2021-22956 only affects access to the management GUI, Nitro API and RPC communication and does not affect CLI access. Citrix strongly recommends that network traffic to the appliance’s management interface is separated, either physically or logically, from normal network traffic. Doing so greatly diminishes the risk of exploitation of this issue. 

See https://docs.citrix.com/en-us/citrix-adc/citrix-adc-secure-deployment/secure-deployment-guide.html for more information. 

What Customers Should Do

To address these vulnerabilities customers should follow all the upgrade and configuration instructions below. 

CVE-2021-22955: Affected customers must upgrade to one of the following supported versions of Citrix ADC and Citrix Gateway to address the vulnerability: 

• Citrix ADC and Citrix Gateway 13.1-4.43 and later releases  
• Citrix ADC and Citrix Gateway 13.0-83.27 and later releases of 13.0 
• Citrix ADC and Citrix Gateway 12.1-63.22 and later releases of 12.1 

• Citrix ADC and NetScaler Gateway 11.1-65.23 and later releases of 11.1 
• Citrix ADC 12.1-FIPS 12.1-55.257 and later releases of 12.1-FIPS 

Citrix recommends that affected customers install the relevant update as soon as possible. 

CVE-2021-22956: Customers must configure their appliance according to the Citrix Application Delivery Controller, Citrix Gateway, and Citrix SD-WAN WANOP Edition – Management Module Configuration Reference Guide to address the vulnerability. This configuration change is only available in the following versions: 

• Citrix ADC and Citrix Gateway 13.1-4.43 and later releases 
• Citrix ADC and Citrix Gateway 13.0-83.27 and later releases of 13.0 
• Citrix ADC and Citrix Gateway 12.1-63.22 and later releases of 12.1 
• Citrix ADC and NetScaler Gateway 11.1-65.23 and later releases of 11.1 
• Citrix ADC 12.1-FIPS 12.1-55.257 and later releases of 12.1-FIPS  
• Citrix SD-WAN WANOP Edition 11.4.2 and later releases of 11.4 
• Citrix SD-WAN WANOP Edition 10.2.9c and later releases of 10.2 

Citrix recommends that affected customers ensure they are running a relevant version and then modify the configuration as soon as their patching schedule allows.