Deserialization of Untrusted Data in Microsoft products - CVE-2026-21511

Vulnerability identifier: #VU122587

CSH Severity: Medium

CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:U/U:Green

CVE-ID: CVE-2026-21511

CWE-ID: CWE-502

Exploitation vector: Remote access

Exploit availability: No public exploit available

Vendor: Microsoft

Affected software:
Microsoft SharePoint Server
Microsoft SharePoint Enterprise Server
Microsoft SharePoint Server Subscription Edition
Microsoft Office
Microsoft Word
Microsoft 365 Apps for Enterprise
Microsoft Office LTSC

The vulnerability allows a remote attacker to compromise the target system.

The vulnerability exists due to insecure input validation when processing serialized data in Microsoft Outlook. A remote attacker can pass specially crafted data to the application and gain access to sensitive information.

Install updates from vendor's website.

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21511