Citrix has patched a critical remote code execution vulnerability in its ADC and Gateway products. This vulnerability has reportedly been exploited as a zero day; organizations should patch urgently.
Background
On December 13, Citrix released a security advisory and accompanying blog for CVE-2022-27518, a critical remote code execution (RCE) vulnerability impacting several supported versions of Citrix Application Delivery Controller (ADC) and Citrix Gateway. Both the advisory and blog post note that targeted attacks have been observed in the wild and customers should patch this vulnerability immediately.
In addition to the blog post, an alert from the National Security Agency (NSA) has been released, providing Citrix users a threat hunting guide. The advisory notes that APT5, also known as UNC2630 and MANGANESE, have been observed targeting Citrix ADCs. The threat hunting guidance it provides can be used to identify if an ADC has been compromised. The guidance is careful to point out that the artifacts discussed could vary based on the stage of compromise
Analysis
CVE-2022-27518 is a RCE vulnerability impacting Citrix ADC or Citrix Gateway when configured as a Security Assertion Markup Language (SAML) service provider (SP) or a SAML identity provider (IdP). The vulnerability is rated as critical and can be exploited by a remote, unauthenticated attacker to execute arbitrary code. At the time of its initial release, CVE-2022-27518 has not received a CVSSv3 score.
Just last month, Citrix patched another critical vulnerability in Citrix ADC and Gateway products. However, vulnerabilities in VPNs are not new, and are quite a common way for threat actors to establish a foothold in target networks. Threat actors routinely leverage vulnerabilities in Citrix ADC and Gateway products, as these technologies are regularly left unpatched. As this vulnerability is being exploited, organizations should patch immediately.
Proof of concept
At the time this blog was released, no proof-of-concept code had been released for CVE-2022-27518.
Vendor response
Citrix has released a patch for affected versions of Citrix ADC and Citrix Gateway. The following table lists the impacted versions and the fixed releases:
| Affected Version | Fixed Version |
|---|---|
| Citrix ADC and Citrix Gateway versions prior to 12.1 | End of life. Upgrade to a supported version |
| Citrix ADC and Citrix Gateway 12.1 before 12.1-65.25 | Citrix ADC and Citrix Gateway 12.1-65.25 and later |
| Citrix ADC and Citrix Gateway 13.0 before 13.0-58.32 | Citrix ADC and Citrix Gateway 13.0-58.32 and later |
| Citrix ADC 12.1-FIPS before 12.1-55.291 | Citrix ADC 12.1-FIPS 12.1-55.291 and later |
| Citrix ADC 12.1-NDcPP before 12.1-55.291 | Citrix ADC 12.1-NDcPP 12.1-55.291 and later |
| Citrix ADC and Citrix Gateway version 13.1 | Not affected |
Solution
The advisory from Citrix notes that customers using Citrix-managed cloud services or Citrix-managed Adaptive Authentication will not need to take any action to address this vulnerability. Citrix users that manage their own Citrix ADC and Citrix Gateway appliances will need to update to address this flaw.
Identifying affected systems
A list of Tenable plugins to identify this vulnerability will appear here as they’re released. This link uses a search filter to ensure that all matching plugin coverage will appear as it is released. Organizations can also use plugin ID 73204 to identify Citrix ADC (formerly NetScaler) devices. A Tenable audit for Citrix ADC best practices is also available.
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