The recent discovery of the CVE-2023-3519 vulnerability in Citrix systems has raised significant concerns in the cybersecurity community. This article provides a comprehensive overview of the vulnerability, its potential impact, and the steps that can be taken to mitigate it.
The Vulnerability
CVE-2023-3519 is a critical vulnerability that affects all Citrix Application Delivery Controller (ADC) and Gateway systems. It allows anonymous remote code execution, enabling unauthenticated attackers to take over various machines with root privileges. The vulnerability was detailed by the Cybersecurity and Infrastructure Security Agency (CISA) in their alert AA23-201A on 20th of July 2023.
Threat Actors Exploiting Citrix CVE-2023-3519 to Implant Webshells
Exploitation
Threat actors have been exploiting this vulnerability to implant web shells on vulnerable systems. These web shells allow attackers to execute arbitrary system commands, effectively giving them control over the compromised system.
The CISA has observed multiple instances of this exploitation, with threat actors using the web shells to perform reconnaissance and lateral movement within the network.
Mitigation
Citrix has released a patch for all supported versions of the ADC and Gateway systems. However, there are no patches for version 12.1 or older as these systems have reached their End of Life (EOL) and will no longer receive the necessary fix. In such cases, it is recommended to update to the latest 13.0 or 13.1 version.
In addition to applying the patch, it is crucial to conduct a thorough review of the systems, even those with protections in place. This is because it is impossible to determine when attacks may have begun before they are widely deployed.
Tools for Detection and Mitigation
Several tools have been developed to help detect and mitigate this vulnerability. One such tool is the Citrix Scanner for CVE-2023-3519 developed by Telekom Security.
This script identifies vulnerable Citrix Gateways/ADCs by looking at the HTTP headers. It is important to note that reverse proxies and heavily customised front pages may alter the results, so this script should not be the only method of checking for vulnerability.
Another tool is the http-vuln-cve2023-3519.nse script developed by RootUp. This script is designed to detect the presence of the CVE-2023-3519 vulnerability in a system.
The CVE-2023-3519 vulnerability poses a significant threat to Citrix systems. However, with the right tools and mitigation strategies, it is possible to protect your systems from this vulnerability.
