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 the following security issues: 

CVE-ID	Description	CWE	Affected Products	Pre-conditions	Criticality
CVE-2021-22955	Unauthenticated denial of service	CWE-400: Uncontrolled Resource Consumption	Citrix ADC, Citrix Gateway	Appliance must be configured as a VPN (Gateway) or AAA virtual server	Critical
CVE-2021-22956	Temporary disruption of the Management GUI, Nitro API and RPC communication	CWE-400: Uncontrolled Resource Consumption	Citrix ADC, Citrix Gateway, Citrix SD-WAN WANOP Edition	Access to NSIP or SNIP with management interface access	Low

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:  Affected customers must upgrade to one of the following supported versions of Citrix ADC and Citrix Gateway to address the vulnerability and must configure their appliance according to Citrix Application Delivery Controller, Citrix Gateway, and Citrix SD-WAN WANOP Edition - Management Module Configuration Reference Guide. to address the vulnerability.

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. 

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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. 

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Instructions

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 

Customers who have configured their Citrix ADC and Citrix Gateway appliances in a high availability (HA) deployment are recommended to update their appliances to the following versions and must configure their appliance according to  Citrix Application Delivery Controller, Citrix Gateway, and Citrix SD-WAN WANOP Edition - Management Module Configuration Reference Guide to address the vulnerability:

• Citrix ADC and Citrix Gateway 14.1 29.63 and later releases
• Citrix ADC and Citrix Gateway 13.1 53.24 and later releases of 13.1
• Citrix ADC 13.1-FIPS 13.1-37.190 and later releases of 13.1-FIPS
• Citrix ADC 12.1-FIPS 12.1-55.325 and later releases of 12.1-FIPS 

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

2025-02-24 T 17:00:00Z

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