Zero-Day Advisory

Fortinet Discovers Web Media Extension Flac Decoder Memory Corruption Vulnerability


Fortinet's FortiGuard Labs has discovered an out-of-bounds memory write vulnerability in Microsoft Web Media Extension.

Web Media Extensions is a new application for Microsoft's Windows 10 operating system that adds support for OGG, Vorbis, and Theora.

The out-of-bounds memory write vulnerability exists due to unsanitized user-controlled data crafted in a OGG file parsed by a vulnerable component. An attacker who successfully exploited the vulnerability could obtain remote code execution on the user's system.


Users should apply the solution provided by Microsoft.


Fortinet reported the vulnerability to Microsoft on January 18, 2021

Microsoft confirmed the vulnerability on April 06, 2021

Microsoft released a patch for the vulnerability on May 11, 2021


This vulnerability was discovered by Wayne Low 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.