CVE-2026-20963 Microsoft SharePoint Deserialization of Untrusted Data Vulnerability
Microsoft SharePoint contains a deserialization of untrusted data vulnerability that allows an unauthorized attacker to execute code over a network.
From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.
Should You Worry?
- CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 18 Mar 2026.
- Rated Critical severity (CVSS 9.8, scored by Vendor).
- This product type is often exposed to the internet, which is where attackers scan for it first.
- It has been in the catalogue for 233 days. Systems still unpatched now have almost certainly been scanned for it.
What It Is
Deserialization of untrusted data in Microsoft Office SharePoint allows an unauthorized attacker to execute code over a network.
Affected Versions
| Product | Versions |
|---|---|
| Microsoft Microsoft SharePoint Enterprise Server 2016 | 16.0.0 to before 16.0.5535.1001 |
| Microsoft Microsoft SharePoint Server 2019 | 16.0.0 to before 16.0.10417.20083 |
| Microsoft Microsoft SharePoint Server Subscription Edition | 16.0.0 to before 16.0.19127.20442 |
From the public CVE record, as supplied by the vendor. Always confirm against the vendor advisory.
What To Do Now
- 1
Find it
Search your asset inventory and external attack surface for Microsoft SharePoint. Include cloud images, appliances and anything a supplier runs for you.
Attack Surface Management - 2
Fix it
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Vulnerability Management - 3
Hunt for compromise
If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.
Incident Response - 4
Prove it is fixed
Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.
Penetration Testing
The Compliance Clock
General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.
Not Sure If You Are Exposed?
Our attack surface and vulnerability teams can check your internet-facing estate for CVE-2026-20963 and every other exploited flaw on the list.