Checklist for Citrix ADC CVE-2019-19781

Citrix has released a critical vulnerability warning (CVE-2019-19781) in all Citrix ADC & Gateway systems one week before Christmas. Several working exploits have been released since Jan. 10, 2020 and are available to everyone.

Important ! The fix from Citrix with the Responder Policy does not work on systems with version 12.1.51.16/51.19, 50.31 and older. If this version is in use, please update to the latest 12.1 version.

The exploits allow remote code to be executed anonymously, allowing unauthenticated attackers to take over the various machines with root privileges.

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Update to Virtual Apps and Desktops Version 1912 LTSR

On December 18, Citrix Virtual Apps and Desktops (CVAD) version 1912 was released. Following a little guide to the update to the latest version.

Link to Citrix Virtual Apps and Desktops Documentation

Citrix Virtual Apps and Desktops EOM EOL Matrix
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Update to Virtual Apps and Desktops Version 1909

On September 19, Citrix Virtual Apps and Desktops (CVAD) version 1909 was released. Following a little guide to the update to the latest version.

Link to Citrix Virtual Apps and Desktops Documentation

Citrix Virtual Apps and Desktops EOM EOL Matrix
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SAML Authentication with Azure AD as IdP and Citrix as SP

Since Citrix XenApp / XenDesktop 7.9 the Federated Authentication Service (FAS) is available. Via Citrix FAS it is possible to authenticate a user via SAML and thus connect Citrix as a service provider to existing identity providers, such as Azure-AD.

Sequence of SAML authentication

  1. The user browse the FQDN (e.g. citrix.deyda.net) of the Citrix Gateway vServer (Service Provider) to start his VA / VD resources
  2. The Citrix Gateway vServer directs the unauthenticated user directly to the Identity Provider (Azure-AD) to authenticate itself (saml: authnRequest)
  3. The Identity Provider points to its SingleSignOnService URL (e.g. login.microsoftonline.com) and the user must authenticate
  4. The user enters his AD credentials and these are checked by the Identity Provider against the user database
  5. Upon successful verification in the user database, the IdP is informed
  6. The IdP issues a token (SAML assertion) and sends it to the Citrix Gateway (saml: response)
  7. Citrix Gateway checks the token (assertion signature) and extracts the UPN from the assertion token. This allows access via SSO to the VA / VD farm via FAS (The SP does not have access to the user’s credentials)
SAML Auth Azure AD & Citrix Gateway with FAS
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Copy a Citrix ADC configuration to a new machine

In one of my recent projects, I had to build several Citrix ADCs in a new data center. After consultation with the customer, the same services and functions should be configured as in the old data center. The only difference was that the new data center should use different IP ranges and therefore all network settings of the Citrix ADCs and the connected services had to be adapted.

Requirements

  • Same version and build on all Citrix ADC
  • Same Citrix ADC license version on all Citrix ADC
  • IP addresses of the new Citrix ADC should be defined and free (NSIP, SNIP & VIP).
  • IP addresses of the connected machines should be known (server or server groups)
  • Basic configuration of the new Citrix ADC should be done (NSIP, SNIP, DNS, Timezone & License)
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