Zero-Day Advisory

Fortinet Discovers Microsoft Windows AppX Deployment Server Elevation of Privilege

Summary

Fortinet's FortiGuard Labs has discovered a local privilege escalation in Microsoft Windows Appx Deployment Service (AppXSvc)

Microsoft Windows Appx Deployment Server is a default Windows 10 service that is responsible to provide infrastructure support for deploying Windows Store applications.

The local elevation of privilege happens when an attacker creates bogus symbolic link for predictable files and folders created by AppXSvc that allows unprivileged users overwrite discretionary access control of escalated files.

Solutions

FortiGuard Labs released the following FortiGate IPS signature which covers this specific vulnerability:

MS.RPC.AppXSvc.Privilege.Escalation
Released Jan 08, 2019

Users should apply the solution provided by Microsoft.

Timeline

Fortinet reported the vulnerability to Microsoft on November 08, 2018.

Microsoft confirmed the vulnerability on December 04, 2018.

Microsoft patched the vulnerability on March 13, 2019.

References

• https://portal.msrc.microsoft.com/en-us/security-guidance/advisory/CVE-2019-0766
  

• CVE-CVE-2019-0766

Acknowledgement

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.