Microsoft SharePoint Server: Information disclosure through incorrect authorization
Summary
CVE-2026-109455 is an incorrect authorization flaw (CWE-863) in the on-premises Microsoft SharePoint Server Subscription Edition. An authenticated attacker with a valid low-privilege account on the network can read information they should not be able to access, with high impact on confidentiality only. Integrity and availability are not affected, and no user interaction is required.
Affected
- Microsoft SharePoint Server Subscription Edition (on-premises): 16.0.0 before 16.0.20326.20278
- Unknown: SharePoint Server 2019 and 2016 (not listed in the CVE record or trackers; do not assume they are unaffected)
- Unknown: SharePoint Online (Microsoft 365)
- Office Online Server is not listed for this CVE
Fixed in
- Build 16.0.20326.20278 or later
- Patch: KB 5002945 for SharePoint Server Subscription Edition, identical to the November 2026 CU
- Note: if the farm is at the September 2025 CU, a PowerShell script to correct folder permissions must be run before installing, otherwise the installation fails. Verify the script and steps against Microsoft's guidance first.
Workaround
Unknown. No CVE-specific workaround or mitigation has been identified. Installing the fix is the recommended measure.
Exploitation
- No evidence of exploitation in the wild found at the time of research (10 Nov 2026).
- Not listed in the CISA KEV catalogue (not fully verified).
- CVSS exploit maturity is E:U (unproven).
- Public proof of concept: Unknown.
Our recommendation
- Check whether on-premises SharePoint Server Subscription Edition is in use and confirm the farm build against 16.0.20326.20278.
- Install KB 5002945 or the November 2026 CU in the normal monthly patch cycle; priority is moderate.
- Check the folder-permission issue before installing if the farm is on the September 2025 CU.
- Keep SharePoint off the public internet and block external access to Central Administration.
- Review accounts with low-privilege access, since a valid account is required for exploitation.
- Confirm separately whether SharePoint 2016/2019 or cloud tenants are affected, and check the MSRC advisory before acting on version numbers.
Information from Microsoft (Patch Tuesday November 2026)
- Severity (Microsoft)
- Important
- Impact
- Information disclosure – Microsoft Office SharePoint
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation less likely
- Product family
- Microsoft Office
- Updates (KB)
- KB5002945
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- CVE record CVE-2026-109455 www.cve.org
- MSRC Security Update Guide msrc.microsoft.com
- Stefan Gossner blog: SharePoint security fixes November 2026 blog.stefan-gossner.com
- OffSeq tracker CVE-2026-109455 radar.offseq.com
- Strix.ai CVE-2026-109455 www.strix.ai
- CISA alert: SharePoint hardening (general, not CVE-specific) www.cisa.gov
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 11 Nov 2026, 12:35.
Original description (NVD)
Incorrect authorization in Microsoft Office SharePoint allows an authorized attacker to disclose information over a network.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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