Security Digest · Vulnerability record · Known exploited
CVE-2026-20963: Microsoft SharePoint Deserialization of Untrusted Data Vulnerability
Exploited in the wild (CISA KEV). Deserialization of untrusted data in Microsoft Office SharePoint allows an unauthorized attacker to execute code over a network.
CISA KEV · added 2026-03-18 CVSS 9.8 Critical EPSS 29.2% · p98
Should you act?
Exploited: patch now if you run it
CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- Yes, if you run Microsoft SharePoint. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-03-18, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-03-21; treat that as the outer limit, not the target.
- EPSS 29.2%, percentile 98: FIRST’s model estimates a 29.2% chance of exploitation activity in the next 30 days, higher than 98% of all scored CVEs (very high). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
What it is
Deserialization of untrusted data in Microsoft Office SharePoint allows an unauthorized attacker to execute code over a network.
CISA’s summary
Microsoft SharePoint contains a deserialization of untrusted data vulnerability that allows an unauthorized attacker to execute code over a network.
Weakness type: CWE-502.
Product: Microsoft SharePoint · Assigned by: microsoft · Published: 2026-01-13
Affected and fixed versions
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| Microsoft | Microsoft SharePoint Enterprise Server 2016 | 16.0.0 < 16.0.5535.1001 |
| Microsoft | Microsoft SharePoint Server 2019 | 16.0.0 < 16.0.10417.20083 |
| Microsoft | Microsoft SharePoint Server Subscription Edition | 16.0.0 < 16.0.19127.20442 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| microsoft | 3.1 | 9.8 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Privileges required: none (no login)
- User interaction: none
- Scope: unchanged
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- CISA KEV: added 2026-03-18; federal due date 2026-03-21. Known ransomware use: Unknown.
- CISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
- CISA SSVC assessment: exploitation active, automatable yes, technical impact total.
- FIRST EPSS (model of 2026-10-21): 29.20% probability of exploitation activity in the next 30 days; percentile 98.
Timeline
- — CVE record published by microsoft
- — Added to CISA’s Known Exploited Vulnerabilities catalog
- — CISA remediation deadline for US federal agencies
- — CVE record last updated
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vendor and project advisories, patches
- Microsoft SharePoint Remote Code Execution Vulnerability msrc.microsoft.com
Vulnerability records
- CVE.org record CVE-2026-20963 cve.org
- NVD entry CVE-2026-20963 nvd.nist.gov
Government
All exploited Microsoft vulnerabilities · Today’s Security Digest