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Citrix ADC, Gateway, and SD-WAN WANOP Security Update  

Jeff Silverman

2 min read

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Critical unauthenticated denial of service, and temporary distribution of management communication are the potential impacts of the latest Citrix vulnerability.


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:


CVD-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


Affected versions

The following supported versions of Citrix ADC and Citrix Gateway are affected by CVE-2021-22955 and CVE-2021-22956:

  • 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


The following supported versions of Citrix SD-WAN WANOP Edition are affected by CVE-2021-22956:

  • Citrix SD-WAN WANOP Edition 11.4 before 11.4.2
  • Citrix SD-WAN WANOP Edition 10.2 before 10.2.9c


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.


Recommended Action

The following supported versions of Citrix ADC and Citrix Gateway address both CVE-2021-22955 and CVE-2021-22956:

  • Citrix ADC and Citrix Gateway 13.1-4.43 and later releases of 13.1
  • 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

The following supported versions of Citrix SD-WAN WANOP Edition address CVE-2021-22956:

  • 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 install the relevant update as soon as possible.


In addition, upon upgrading to a fixed version, customers must modify the device configuration to resolve CVE-2021-22956. See Citrix Application Delivery Controller, Citrix Gateway, and Citrix SD-WAN WANOP Edition – Management Module Configuration Reference Guide for details.  


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