Zero-Day Advisory

Fortinet Discovers Citrix Receiver DLL Preloading Vulnerability

Summary

Fortinet's FortiGuard Labs has discovered a DLL preloading vulnerability in Citrix Receiver.

Citrix Receiver is the client component of XenDesktop or XenApp. Devices with Receiver installed are able to access full desktops via XenDesktop or individual applications via XenApp from a centralized host, such as a server or cloud infrastructure.

Citrix Receiver for Windows is susceptible to a DLL preloading vulnerability. The issue occurs when the application looks to load a DLL for execution and an attacker provides a malicious DLL to use instead. The application generally follows a specific search path to locate the DLL. The vulnerability can be exploited by a simple file write (or potentially an over-write) which results in a foreign DLL running under the context of the application.

Solutions

Users should apply the solution provided by Citrix Systems.

Timeline

Fortinet reported the vulnerability to Citrix Systems on June 4, 2017.

Citrix Systems confirmed the vulnerability on July 28, 2017.

Citrix Systems patched the vulnerability on August 18, 2017.

Acknowledgement

This vulnerability was discovered by Kushal Arvind Shah of Fortinet's FortiGuard Labs.

IPS Subscription

Fortinet customers who subscribe to Fortinet's intrusion prevention (IPS) service should be protected against this vulnerability with the appropriate configuration parameters in place. Fortinet's IPS service is one component of FortiGuard Subscription Services, which also offer comprehensive solutions such as antivirus, Web content filtering and antispam capabilities. These services enable protection against threats on both application and network layers. FortiGuard Services are continuously updated by FortiGuard Labs, which enables Fortinet to deliver a combination of multi-layered security intelligence and true zero-day protection from new and emerging threats. These updates are delivered to all FortiGate, FortiMail and FortiClient products. Fortinet strictly follows responsible disclosure guidelines to ensure optimum protection during a threat's lifecycle.