Microsoft SharePoint Server: Remote code execution via deserialization
Summary
An on-premises Microsoft SharePoint Server Subscription Edition is affected by a deserialization flaw (CWE-502) that allows an authorized attacker to execute code over the network. The CVSS vector assumes low privileges and flags a scope change, so any compromised, phished or self-registered account could be used. The risk is highest if SharePoint is reachable from the internet. The public wording does not state the required privilege level, so the ZDI review advises assuming default permissions.
Affected
- Microsoft SharePoint Server Subscription Edition (x64), 16.0.0 before 16.0.20326.20190
- SharePoint 2016 and 2019: Unknown. The CNA data lists only Subscription Edition.
Fixed in
- Build 16.0.20326.20190 or later, shipped with KB5002927 (October 2026 cumulative update, October 13, 2026)
- Unverified: the CVE number was not confirmed in the KB text reviewed. Check the MSRC page or the KB CVE table.
Workaround
- No CVE-specific workaround known. Patching is the fix.
- General CISA SharePoint hardening: do not expose SharePoint directly to the internet; if exposure is unavoidable, use a Layer 7 reverse proxy that enforces authentication; enable AMSI for each web application; block external access to Central Administration.
Exploitation
- Not listed in the CISA KEV catalogue at last check (third-party source; re-check CISA).
- EPSS about 0.0095 (low).
- No public proof of concept or exploitation found.
- Do not confuse with CVE-2026-45659, a different SharePoint deserialization RCE that CISA lists as exploited.
Our recommendation
- Check whether any client runs SharePoint Server Subscription Edition on-premises.
- Apply KB5002927 (October 2026 cumulative update) and verify the build is 16.0.20326.20190 or later.
- If SharePoint is internet-facing or unpatched, treat as high priority: limit exposure first, then patch.
- Review accounts with access to SharePoint, including self-registered and external accounts, and enforce strong authentication.
- Monitor SharePoint and IIS logs for unusual requests and new processes spawned by the SharePoint application pool.
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
- Microsoft Security Update Guide (CVE-2026-105013) msrc.microsoft.com
- Microsoft KB5002927 support.microsoft.com
- Microsoft SharePoint updates (Learn) learn.microsoft.com
- CVE record mirror (Vulners) vulners.com
- CISA: SharePoint hardening alert (July 2026) www.cisa.gov
- Zero Day Initiative October 2026 security update review www.zerodayinitiative.com
- October 2026 CU for SharePoint Server Subscription Edition (Stefan Gossner) blog.stefan-gossner.com
- Senserva KB5002927 summary senserva.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 3 Nov 2026, 01:08.
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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