Advisory Details

January 14th, 2021

Microsoft Windows AppX Deployment Service Directory Junction Privilege Escalation Vulnerability

ZDI-21-025
ZDI-CAN-12170

CVE ID CVE-2021-1685
CVSS SCORE 7.0, (AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H)
AFFECTED VENDORS Microsoft
AFFECTED PRODUCTS Windows
VULNERABILITY DETAILS

This vulnerability allows local attackers to escalate privileges on affected installations of Microsoft Windows. An attacker must first obtain the ability to execute low-privileged code on the target system in order to exploit this vulnerability.

The specific flaw exists within the AppX Deployment Service. By creating a directory junction, an attacker can abuse the service to create files. An attacker can leverage this vulnerability to escalate privileges and execute arbitrary code in the context of SYSTEM.

ADDITIONAL DETAILS Microsoft has issued an update to correct this vulnerability. More details can be found at:
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-1685
DISCLOSURE TIMELINE
  • 2020-10-30 - Vulnerability reported to vendor
  • 2021-01-14 - Coordinated public release of advisory
CREDIT JeongOh Kyea (@kkokkokye) of THEORI
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