What is CVE-2026-20963?
Remote code execution vulnerability in Microsoft SharePoint Server caused by unsafe deserialization of untrusted data (CWE-502). The flaw resides in handling of serialized objects within ASP.NET ViewState and related serialized data streams processed by SharePoint application pages under the /_layouts/ directory. An attacker with low-level authentication can craft a malicious serialized payload using gadget chains to execute arbitrary code in the context of the SharePoint application pool process (w3wp.exe). Patched in January 2026 Patch Tuesday. CISA KEV added 2026-03-18 with remediation deadline 2026-03-21.
The record classifies CVE-2026-20963 under weakness class CWE-502. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs low-privilege credentials, needs no user interaction, and has high impact on confidentiality, integrity, availability. 6 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 295 days ago.
Severity and exploitation probability
- CVSS v3.1 base score
- 8.8 — HIGH
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H - EPSS (FIRST)
- 29.2% probability of exploitation in the next 30 days, higher than 98.1% of all scored CVEs
- CISA KEV
- Listed since 2026-03-18, federal remediation deadline 2026-03-21
- Threadlinqs priority
- 9/10 — CISA KEV-listed, which Threadlinqs floors at 9
- Published
- 2026-01-13, last modified 2026-07-30
Is CVE-2026-20963 being exploited?
CISA added CVE-2026-20963 to the Known Exploited Vulnerabilities catalog on 2026-03-18, which means the agency holds evidence of exploitation in the wild; US federal civilian agencies had to remediate it by 2026-03-21 under BOD 22-01. It currently carries a trending score of 40 in the Threadlinqs vulnerability feed.
Affected products and versions
- (vendor unspecified): Microsoft SharePoint Server 2007, Microsoft SharePoint Server 2010, Microsoft SharePoint Server 2013, Microsoft SharePoint Server 2016, Microsoft SharePoint Server 2019, Microsoft SharePoint Server Subscription Edition
How to fix CVE-2026-20963
Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20963. Because CVE-2026-20963 is KEV-listed, US federal civilian agencies were required to apply the vendor fix, or stop using the product, by 2026-03-21. Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.
Threat activity tracking CVE-2026-20963
1 tracked threat in the Threadlinqs corpus references CVE-2026-20963, either in the campaign’s CVE list or as an indicator on the campaign record.
- Microsoft SharePoint Server Deserialization RCE (CVE-2026-20963) — CISA KEV Active Exploitation — CRITICAL · 2026-03-21
Sources
Enriched from CVE.org, FIRST EPSS, CISA KEV. Last verified by Threadlinqs on .