Zero-Day Advisory

Fortinet Discovers Tresorit for Windows DLL PreLoading Vulnerability


Fortinet's FortiGuard Labs has discovered a DLL preloading vulnerability in Tresorit for Windows.

Tresorit is an online cloud storage service that emphasizes enhanced security and data encryption for businesses and individuals/freelancers. It offers extra security features such as DRM, granular access levels and other functions which aim to create a safer collaborative environment. Tresorit is accessible through client desktop software, web-based application and mobile apps namely, Windows, macOS, Android, Windows Phone 8, iOS, and Linux.

Tresorit 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.


Users should apply the solution provided by Tresorit.


Fortinet reported the vulnerability to Tresorit on May 06, 2018.

Tresorit confirmed the vulnerability on May 07, 2018.

Tresorit released patch for it on May 18, 2018.


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.