SRC-2021-0016 : Microsoft SharePoint Server InputFormRegularExpressionValidator Denial of Service Vulnerability

CVE ID: CVE-2021-28450

CVSS Score: 5.0, (/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:L)

Affected Vendors: Microsoft

Affected Products: SharePoint Server

Vulnerability Details:

This vulnerability allows remote attackers to cause a denial of service on affected installations of SharePoint Server. Authentication is required to exploit this vulnerability.

The specific flaw exists within the InputFormRegularExpressionValidator class. The issue results from the lack of proper validation of the user-supplied ValidationExpression property. An attacker can leverage this vulnerability to cause a regular expression denial of service.

Vendor Response:

Microsoft has issued an update to correct this vulnerability. More details can be found at:

Disclosure Timeline:

  • 2021-01-11 – Sent to Microsoft

  • 2021-04-13 – Coordinated public release of advisory

Credit: This vulnerability was discovered by Yuhao Weng and Zhiniang Peng of Sangfor and Steven Seeley of Qihoo 360 Vulcan Team