Zero-Day Advisory

Fortinet Discovers Windows MSI Signature Spoofing Vulnerability


Fortinet's FortiGuard Labs has discovered a vulnerability to bypass Windows Installer (MSI) Authenticode signature validation.

Windows Installer is a software component and application programming interface (API) of Microsoft Windows used for the installation, maintenance, and removal of software. The installation information, and optionally the files themselves, are packaged in installation packages, loosely relational databases structured as COM Structured Storages and commonly known as "MSI files", from their default filename extensions.

A bypass vulnerability has been discovered in Windows Installer Authenticode signature validation. The vulnerability exists due to the signature computation mechanism. It could allow an attacker to disguise an altered MSI as legitimate installer.


Users should apply the solution provided by Microsoft.


Fortinet reported the vulnerability to Microsoft on July 21, 2021.

Microsoft confirmed the vulnerability on July 30, 2021.

Microsoft patched the vulnerability on October 12, 2021.


This vulnerability was discovered by Asaf Rubinfeld 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.