Summary
Impact: Elevation of Privilege. Microsoft rating: Critical. Not known to be exploited — Exploitation Less Likely. Customer action: Required.
Details
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.
Security updates
16.0.20326.20190 — https://support.microsoft.com/help/5002927
Vulnerabilities 1
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High 8.1
Microsoft Office SharePoint Elevation of Privilege Vulnerability
Improper verification of cryptographic signature in Microsoft Office SharePoint allows an unauthorized attacker to elevate privileges over a network.
Revision history
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#1
Information published.
References
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CVE-2026-102866 Microsoft Office SharePoint Elevation of Privilege Vulnerability - HTML
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-102866
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Microsoft Exploitability Index
https://www.microsoft.com/en-us/msrc/exploitability-index?rtc=1
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Microsoft Support Lifecycle
https://support.microsoft.com/lifecycle
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Common Vulnerability Scoring System
https://www.first.org/cvss