On Tuesday, December 13, a joint announcement from the United States NSA and Citrix announced a zero-day vulnerability in Citrix ADC. The vulnerability (CVE-2022-27518) is a critical unauthenticated Remote Code Execution (RCE) issue currently rated as CVSS 9.8. Patches are already available from Citrix. The NSA attributes the zero-day to APT5, a Chinese hacking collective. There is currently no guidance for how widespread the campaign has been or how long it's been ongoing.
The vulnerability affects the following Citrix ADC and Citrix Gateway versions:
Additionally, these instances must be configured with SAML SP or IdP to be affected. You can check if your Citrix ADC or Citrix Gateway is configured as a SAML SP or a SAML IdP by inspecting the ns.conf file for the following commands:
If either of the commands is present and if the version is one of the affected versions listed above, you should patch as soon as possible.
We recommend administrators patch all affected systems as soon as possible, especially if publicly exposed. If patching is not an immediate option, administrators should consider placing their affected systems behind a firewall/VPN and segmenting the systems away from other networks to minimize the spread of damage in the case of a compromise.
For more information on the vulnerability and the mitigations that Citrix has released, please view its blog here with recommended next steps. Additionally, the U.S. NSA has released a Threat Hunt guide with potential behavioral artifacts that may indicate compromise.
We are diligently monitoring the situation for exposure and associated attacks. As new information is released, we will update this blog.