Advisory Details

September 16th, 2021

Microsoft Windows Update Agent Directory Junction Privilege Escalation Vulnerability

ZDI-21-1075
ZDI-CAN-13765

CVE ID CVE-2021-38634
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 Windows Update Agent. By creating a directory junction, an attacker can abuse Windows Update Agent to delete a file. 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-2021-38634
DISCLOSURE TIMELINE
  • 2021-06-08 - Vulnerability reported to vendor
  • 2021-09-16 - Coordinated public release of advisory
CREDIT Abdelhamid Naceri
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