CVE-2026-20963: Microsoft SharePoint Deserialization of Untrusted Data Vulnerability

Is it exploited?

Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 18 Mar 2026, 64 days after the CVE record was published.

How likely is exploitation in the next 30 days?

29.2%

EPSS score, percentile 98.2 of all scored records

How severe?

9.8 Critical

CVSS v3.1 base score, given by the CNA

What should I do?

Required action (CISA), due 21 Mar 2026: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Advisories and patches (1)

Which versions are affected?

Affected: 16.0.0 up to, not including, 16.0.5535.1001; 16.0.0 up to, not including, 16.0.10417.20083; 16.0.0 up to, not including, 16.0.19127.20442

Versions by product

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

What to do

CISA due date for this action: 21 March 2026.

Advisories and patches

• Microsoft SharePoint Remote Code Execution Vulnerability (Vendor advisory, Patch)

Linked from CISA's catalog entry

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20963
• https://nvd.nist.gov/vuln/detail/CVE-2026-20963

Affected products and versions

As listed in the CVE record.

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

About this vulnerability

Microsoft SharePoint contains a deserialization of untrusted data vulnerability that allows an unauthorized attacker to execute code over a network.

Summary: CISA's KEV catalog, as of 28 Oct 2026.

• CISA added CVE-2026-20963 to its Known Exploited Vulnerabilities (KEV) catalog on 18 Mar 2026.
• CISA's ransomware flag for this entry is "Unknown": no evidence of ransomware use in the catalog, which is not proof of none.
• The due date CISA sets for the required action is 21 Mar 2026.
• The CVE record was published on 13 Jan 2026, 64 days before it was added to KEV.
• The CVE record carries a CVSS v3.1 base score of 9.8 (Critical), given by its CNA.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 29.2% (percentile 98.2), as of 28 Oct 2026.
• CISA's SSVC assessment in the CVE record: exploitation active, automatable yes, technical impact total.

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026. About the data.

Description

Microsoft SharePoint Remote Code Execution Vulnerability

Deserialization of untrusted data in Microsoft Office SharePoint allows an unauthorized attacker to execute code over a network.

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

Weakness

• CWE-502: Deserialization of Untrusted Data

CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.

Timeline

More exploited Microsoft vulnerabilities

• CVE-2026-96951: Microsoft Windows Command Injection Vulnerability (added 13 Oct 2026)
• CVE-2026-65660: Microsoft SharePoint Code Injection Vulnerability (added 25 Sep 2026)
• CVE-2026-81963: Microsoft Windows Link Following Vulnerability (added 8 Sep 2026)
• CVE-2026-85880: Microsoft Windows Heap-Based Buffer Overflow Vulnerability (added 8 Sep 2026)
• CVE-2019-1068: Microsoft SQL Server Remote Code Execution Vulnerability (added 26 Aug 2026)
• CVE-2026-33824: Microsoft Internet Key Exchange (IKE) Service Extensions Double Free Vulnerability (added 18 Aug 2026)