CVE-2026-20963
Microsoft SharePoint Deserialization of Untrusted Data Vulnerability
Does this matter?
Known to be exploited in the wild (CISA KEV, CISA remediation deadline 21 March 2026). Treat as an emergency change: patch or isolate now, then hunt for prior compromise.
Description
Deserialization of untrusted data in Microsoft Office SharePoint allows an unauthorized attacker to execute code over a network.
- CVSS 3.1
- 9.8 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- EPSS
- 29.20% probability · 98th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Listed 18 March 2026 · due 21 March 2026
- Weakness
- CWE-502
- Affected
- microsoft/sharepoint server
- Source
- secure@microsoft.com
EPSS moved from 29.6% on 24 September 2026 to 29.2% on 27 October 2026. The dashed line is the ten per cent mark our analysts treat as “patch before the next change window”.
CISA notes
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20963 ; https://nvd.nist.gov/vuln/detail/CVE-2026-20963
References
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.