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CVE-2026-58644 – Remote Code Execution via Deserialization – Microsoft SharePoint Server (Enterpr…

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Summary

CVE-2026-58644 is a critical Remote Code Execution (RCE) vulnerability in Microsoft SharePoint Server, rooted in insecure deserialization of untrusted data (CWE-502). The flaw affects Microsoft SharePoint Enterprise Server 2016, SharePoint Server 2019, and SharePoint Server Subscription Edition, and carries a CVSS v3.1 base score of 9.8 (Critical). Because it requires no authentication and no user interaction, any internet-exposed SharePoint instance running a vulnerable version is at risk of full remote code execution by an unauthenticated attacker.

Technical details

  • Root cause: Deserialization of untrusted data (CWE-502) within Microsoft Office SharePoint’s server-side processing logic.
  • Trigger conditions: An unauthenticated attacker sends a specially crafted network request to a vulnerable SharePoint endpoint; no privileges and no user interaction are required.
  • Attack vector: Network-accessible (AV:N); the vulnerability is exploitable directly over the internet against any exposed SharePoint instance without prior access or credentials (PR:N, UI:N, AC:L).
  • Impact: Successful exploitation allows the attacker to execute arbitrary code on the underlying server, resulting in complete compromise of confidentiality, integrity, and availability (C:H/I:H/A:H). Full system takeover is a potential outcome.

Affected software

  • Microsoft SharePoint Enterprise Server 2016 (x64) — versions prior to 16.0.5556.1005
  • Microsoft SharePoint Server 2019 (x64) — versions prior to 16.0.10417.20153
  • Microsoft SharePoint Server Subscription Edition (x64) — versions prior to 16.0.19725.20384

Severity

  • CVSS v3.1 Base Score: 9.8 (Critical)
  • Vector String: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Patch immediately: Apply the security updates released by Microsoft on July 14, 2026:
    • SharePoint Enterprise Server 2016 → update to 16.0.5556.1005 or later
    • SharePoint Server 2019 → update to 16.0.10417.20153 or later
    • SharePoint Server Subscription Edition → update to 16.0.19725.20384 or later
  • If immediate patching is not feasible: Restrict network access to SharePoint servers at the perimeter — block untrusted external traffic to SharePoint endpoints via firewall or WAF rules until the patch can be applied.
  • Inventory exposure: Identify all internet-facing SharePoint Server deployments and prioritize them for patching; internal-only instances should also be patched but present a lower immediate risk.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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