What is CVE-2026-33827?
An insecure deserialization vulnerability in the SharePoint Server workflow engine allows an authenticated remote attacker to achieve code execution on the SharePoint server. The flaw resides in the workflow activity processing pipeline where untrusted serialized objects are deserialized without adequate type validation. Threat actors have been observed chaining this vulnerability with CVE-2026-32201 (SharePoint spoofing zero-day) to escalate from unauthenticated session hijack to full server-side code execution against enterprise SharePoint farms.
The record classifies CVE-2026-33827 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. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 197 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)
- 0.5% probability of exploitation in the next 30 days, higher than 43.8% of all scored CVEs
- CISA KEV
- Not listed in the CISA Known Exploited Vulnerabilities catalog
- Threadlinqs priority
- 8.2/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- Published
- 2026-04-14, last modified 2026-09-25
Is CVE-2026-33827 being exploited?
Weaponised exploit code for CVE-2026-33827 is publicly available. 1 public proof-of-concept repository is tracked for this identifier. It currently carries a trending score of 24 in the Threadlinqs vulnerability feed.
- kaleth4/CVE-2026-33827 (github)
Affected products and versions
- Microsoft: SharePoint Server
How to fix CVE-2026-33827
The record marks a vendor fix as available for CVE-2026-33827. Patch reference: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-33827. Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-33827. 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-2026-33827
3 tracked threats in the Threadlinqs corpus reference CVE-2026-33827, either in the campaign’s CVE list or as an indicator on the campaign record.
- Microsoft's MDASH AI Scanning Harness Uncovers 16 Windows CVEs, Including Four Critical RCE Flaws in TCP/IP, IKEv2, Netlogon, and DNS — CRITICAL · 2026-07-10
- Microsoft April 2026 Patch Tuesday — 163 CVEs / 88 Advisories (CVE-2026-32201 SharePoint Zero-Day Exploited In-The-Wild, CVE-2026-33825 Defender EoP Public PoC, CVE-2026-33824 IKE RCE CVSS 9.8, CVE-2026-33827 TCP/IP Wormable RCE) — CRITICAL · 2026-04-19
- Microsoft April 2026 Patch Tuesday — 167 Flaws, 2 Zero-Days (SharePoint Spoofing CVE-2026-32201 + Defender EoP CVE-2026-33825) — CRITICAL · 2026-04-14
Sources
Enriched from CVE.org, NVD, FIRST EPSS, public proof-of-concept repositories. Last verified by Threadlinqs on . This product uses the NVD API but is not endorsed or certified by the NVD.