SRC-2021-0013 : Microsoft Exchange Server DlpUtils AddTenantDlpPolicy ruleParameters TOCTOU Remote Code Execution Vulnerability (patch bypass)

CVE ID: CVE-2021-26412

CVSS Score: 9.1, (/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:H/E:P/RL:O/RC:C)

Affected Vendors: Microsoft

Affected Products: Exchange Server

Vulnerability Details:

This vulnerability allows remote attackers to execute arbitrary code on affected installations of Exchange Server. Authentication with the “Data Loss Prevention” role is required to exploit this vulnerability.

The specific flaw exists within the processing of the New-DlpPolicy cmdlet. The issue results from the lack of proper validation of user-supplied ruleParameters when creating a dlp policy. An attacker can leverage this vulnerability to execute code in the context of SYSTEM.

Vendor Response:

Microsoft has issued an update to correct this vulnerability. More details can be found at: https://portal.msrc.microsoft.com/security-guidance/advisory/CVE-2021-26412

Disclosure Timeline:

• 2020-12-09 – Sent to Microsoft

• 2021-03-09 – Coordinated public release of advisory

Credit: This vulnerability was discovered by Steven Seeley (mr_me) of Qihoo 360 Vulcan Team