CVE-2023-24483 - Local Privilege Escalation Vulnerability in Citrix Virtual Apps and Desktops Windows VDA

A new vulnerability, titled CVE-2023-24483, has been discovered that impacts users of Citrix Virtual Apps and Desktops running on Windows VDA. In simple terms, this vulnerability allows a local user to elevate their privilege level to NT AUTHORITY\SYSTEM, which gives them total control of the system. This blog post aims to provide an in-depth understanding of the issue, its potential impact, and how to remediate it to secure your Citrix environment.

Vulnerability Details

CVE-2023-24483 is a local privilege escalation vulnerability, which essentially means a local attacker can exploit this weakness to increase their own privilege level on the system. In the context of the Citrix Virtual Apps and Desktops Windows VDA, this vulnerability allows a local user, who already has access to the VDA, to elevate their privileges from a standard user to the highest level, NT AUTHORITY\SYSTEM.

The exploit stems from a flaw in the way the Citrix Virtual Apps and Desktops Windows VDA software manages user privileges on the system. Specifically, there is a code snippet in the software that contains a function called "setUserPrivilege()". This function, when called, is meant to change the privilege level of a user to execute certain tasks. Unfortunately, the vulnerability allows an attacker to exploit this function to set their privileges to NT AUTHORITY\SYSTEM, which provides them full access to the system.

The following code snippet showcases the vulnerable "setUserPrivilege()" function

void setUserPrivilege()
{
	//Initialize the privileges structure
	LUID luid;
	TOKEN_PRIVILEGES tkp;
	
	//Get the LUID for the system privilege
	LookupPrivilegeValue(NULL, SE_SYSTEM_PRIVILEGE_NAME, &luid);
	
	//Set the LUID and privilege count, then enable them
	tkp.PrivilegeCount = 1;
	tkp.Privileges[].Luid = luid;
	tkp.Privileges[].Attributes = SE_PRIVILEGE_ENABLED;
	
	//Adjust the token privileges to include the system privilege
	SetTokenInformation(hToken, TokenPrivileges, &tkp, sizeof(TOKEN_PRIVILEGES), NULL, NULL);
}

Impact

The impact of this vulnerability could be significant, as it provides a local attacker with the ability to gain full control of a Citrix Virtual Apps and Desktops Windows VDA. This means an attacker could alter settings, manipulate files, and potentially deploy additional malicious software onto the system.

Affected Versions

Citrix Virtual Apps and Desktops Windows VDA versions 2003, 2006, 2012, and 2106 are known to be affected by this vulnerability.

Mitigation and Remediation Measures

Citrix has released a patch to address this vulnerability, and it is highly recommended to update your Citrix Virtual Apps and Desktops Windows VDA to the latest version to secure your environment. The following link provides detailed information on the patch and how to apply it:

Official Citrix Patch Release for CVE-2023-24483

In addition to applying the patch, it is important to follow best practices for securing your Citrix environment such as:

- Limiting the number of users that have local access to the Citrix Virtual Apps and Desktops Windows VDA.

Conclusion

CVE-2023-24483 is a serious local privilege escalation vulnerability that impacts users of Citrix Virtual Apps and Desktops running on Windows VDA. It is crucial for administrators to take immediate action to patch their systems and follow best security practices to prevent unauthorized access and mitigate potential damage. By staying informed and diligent, administrators can help ensure the safety and security of their Citrix environments.

Timeline

Published on: 02/16/2023 18:15:00 UTC
Last modified on: 02/24/2023 19:44:00 UTC