CVE-2026-102866: Microsoft Office SharePoint Elevation of Privilege Vulnerability

Overview

Severity
High (CVSS 8.1)
CVSS Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
Category
Elevation of Privilege
Exploit Status
Not Exploited
Exploitation Likelihood
Less Likely
Patch Tuesday
2026-Oct
Released
2026-10-13

Description

Improper verification of cryptographic signature in Microsoft Office SharePoint allows an unauthorized attacker to elevate privileges over a network.

FAQ

Is the Preview Pane an attack vector for this vulnerability? No, the Preview Pane is not an attack vector. How could an attacker exploit this vulnerability? An unauthenticated attacker who obtains a valid proof token for a targeted user could modify the token and submit it to an affected SharePoint server. Successful exploitation could allow the attacker to authenticate as that user and access or modify content available to the compromised account. User interaction is not required. According to the CVSS metric, the attack complexity is high (AC:H). What does this mean for this vulnerability? An attacker would need specific conditions to be in place (i.e. particular protocol settings, or configurations, etc.) before an attack could succeed, which reduces the likelihood of widespread or opportunistic exploitation.

Affected Products (1)

Microsoft Office

  • Microsoft SharePoint Server Subscription Edition

Security Updates (1)

Acknowledgments

<a href="https://www.linkedin.com/in/mateusz-mto-gierblinski/">Mateusz Gierblinski</a> with <a href="https://curios-it.eu/">Curios</a>

Revision History

  • 2026-10-13: Information published.