Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability
Microsoft — Microsoft SharePoint Enterprise Server 2016
Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.
8.8
76.1%
Vector breakdown
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Published
- May 22, 2026
- Modified
- Jul 23, 2026
- Added to KEV
- Jul 1, 2026
- Federal patch due
- Jul 4, 2026
CISA required action
Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
Weakness classification
Affected packages
Proof-of-concept & exploitation references
2 foundWeaponization
Public repositories whose name or description references CVE-2026-45659, found via a live GitHub search at request time. These are community-sourced signals, not a verified working exploit - cross-check each one before relying on it, and treat higher star counts and recent activity as (weak) corroboration, not proof.
- WismanSec/sharepoint-2026-poc★ 2
PoC, IOCs, and detection logic for the SharePoint /_trust WS-Federation BinaryFormatter deserialization chain. Lab reconstruction covering unauthenticated RCE, in-process machine key theft, and the artifacts each variant leaves behind. SharePoint 2016, 2019, and Subscription Edition. CVE-2026-50522, CVE-2026-45659, CVE-2026-56164, CVE-2026-58644.
updated Aug 19, 2026
- HORKimhab/CVE-2026-45659★ 1
CVE-2026-45659
updated Jul 25, 2026
References
How this class of flaw gets exploited
Frequently asked questions
What is CVE-2026-45659?
Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.
How severe is CVE-2026-45659?
CVE-2026-45659 has a CVSS base score of 8.8 out of 10 (CVSS 3.1).
Is CVE-2026-45659 actively exploited in the wild?
Yes. CVE-2026-45659 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added Jul 1, 2026, meaning CISA has confirmed evidence of active exploitation. It is also flagged as used in ransomware campaigns.
What is the EPSS score for CVE-2026-45659?
76.1% - meaning FIRST.org's EPSS model estimates a 76.1% probability this vulnerability will be exploited in the wild within 30 days (99% percentile among all scored CVEs).
Is there exploit tooling available for CVE-2026-45659?
We found 2 public GitHub repositories referencing CVE-2026-45659, though none matched a known Nuclei template or Metasploit module at last check. Review each one before relying on it - see the proof-of-concept section above.
What type of vulnerability is CVE-2026-45659?
CVE-2026-45659 is classified under CWE-502 (CWE-502: Deserialization of Untrusted Data).
Cross-checked against
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