Improper Verification of Cryptographic Signature in Microsoft SharePoint Server - CVE-2026-102866
Published: October 13, 2026
Vulnerability identifier: #VU154300
CSH Severity: High
CVSS v4: 9.2 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-102866
CWE-ID: CWE-347
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to escalate privileges.
The vulnerability exists due to improper verification of cryptographic signatures in Microsoft Office SharePoint when verifying proof tokens. A remote attacker can obtain a valid proof token for a targeted user, modify it, and submit it to an affected SharePoint server to escalate privileges.
Successful exploitation requires specific protocol settings or configurations to be in place. User interaction is not required.
Affected software
Microsoft SharePoint Server
How to mitigate CVE-2026-102866
Install security update from vendor's website.
Microsoft SharePoint Server - update to 16.0.20326.20190