Threat Intelligence / CVE / CVE-2026-20963

CVE-2026-20963 — Microsoft SharePoint Server 2007

CISA KEV

CVSS v3.1 8.8 (HIGH) · EPSS 6.4% (higher than 91.2% of all scored CVEs) · Priority 9/10 · Published 2026-01-13

As of 2026-04-01, CVE-2026-20963 is a HIGH-severity vulnerability in Microsoft SharePoint Server 2007, CVSS v3.1 8.8, EPSS 6.4% (91.2th percentile). It is listed in the CISA Known Exploited Vulnerabilities catalog (added 2026-03-18), with a US federal remediation deadline of 2026-03-21. Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-20963, most recently “Microsoft SharePoint Server Deserialization RCE (CVE-2026-20963) — CISA KEV Active Exploitation”.

Last updated: 2026-04-01

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 243 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): 6.4% probability of exploitation in the next 30 days, higher than 91.2% 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 2026-04-01

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 38 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

Seeded from threat-derived and not yet processed by the Threadlinqs enrichment pipeline, so blank CVSS, EPSS or KEV fields above mean NOT MEASURED rather than measured-absent.

Full detection coverage & IOCs for threats exploiting CVE-2026-20963 are available via the Threadlinqs MCP server (Purple tier). View plans →

← all vulnerabilities · Markdown version · Threadlinqs Intelligence