Microsoft SharePoint Server: Remote code execution via deserialization
Summary
A deserialization flaw (CWE-502) in on-premises Microsoft SharePoint Server Subscription Edition allows code execution over the network. An attacker needs a valid account with low privileges, such as a Site Member account or a compromised staff account. NVD lists a CVSS base score of 8.8; VulDB lists 6.3 and CWE-94.
Affected
- Microsoft SharePoint Server Subscription Edition: 16.0.0 to before 16.0.20326.20190
- Unconfirmed: SharePoint Server 2016 and 2019
Fixed in
- SharePoint Server Subscription Edition: build 16.0.20326.20190 via security update KB5002927 (October 13, 2026), which replaces KB5002908
- Fix status for SharePoint Server 2016 and 2019: Unknown.
Workaround
Unknown. No vendor workaround was found for this CVE.
Exploitation
- Not known to be exploited in the wild. The CNA's SSVC data records exploitation: none and automatable: no.
- No public proof of concept found.
- Not listed in CISA KEV in the tracker snapshots, which should be rechecked.
- EPSS: about 0.015 (Vulners).
Our recommendation
- Install KB5002927 and the October 2026 cumulative update on all Subscription Edition farms as a priority.
- Check whether any SharePoint farm is published to the internet, for example via reverse proxy or remote access, and restrict such access.
- Review site membership grants and enforce multi-factor authentication to reduce account takeover risk.
- Verify the fix status for SharePoint 2016 and 2019 with Microsoft via the MSRC entry.
- Monitor logs for unusual activity on SharePoint servers.
Information from Microsoft (Patch Tuesday October 2026)
- Severity (Microsoft)
- Important
- Impact
- Remote code execution – Microsoft Office SharePoint
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation less likely
- Product family
- Microsoft Office
- Updates (KB)
- KB5002927
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- MSRC Security Update Guide: CVE-2026-85900 msrc.microsoft.com
- OpenCVE: CVE-2026-85900 (NVD/CNA data) app.opencve.io
- Microsoft KB5002927 support.microsoft.com
- Microsoft SharePoint update history learn.microsoft.com
- VulDB: CVE-2026-85900 vuldb.com
- Senserva KB summary 5002927 senserva.com
- Zero Day Initiative: October 2026 security update review www.zerodayinitiative.com
- Computerworld: October 2026 Patch Tuesday www.computerworld.com
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 31 Oct 2026, 18:20.
Original description (NVD)
Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code 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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