CVE-2026-58644 — Sharepoint Server
CRITICALCVE-2026-58644 is a critical-severity (CVSS 9.8) Deserialization of Untrusted Data vulnerability in microsoft sharepoint server. It is in CISA's Known Exploited Vulnerabilities catalog (added 2026-07-16) — treat it as actively exploited and patch now. A fix is available — see the affected versions and patch details below.
Deserialization of untrusted data in Microsoft Office SharePoint allows an unauthorized attacker to execute code over a network.
Exploitation Status
Actively exploited in the wild
- Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2026-07-16. Federal agencies were required to remediate by 2026-07-19.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2026-58644.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-58644 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the 10–50% band (highlighted). Counts from FIRST.org, log-scaled.
Description
Deserialization of untrusted data in Microsoft Office SharePoint allows an unauthorized attacker to execute code over a network.
Affected Products
sharepoint servermicrosoftDetection & mitigation playbook
Vendor / applianceDetect
Inventory every microsoft sharepoint server deployment and check each version against the affected-products list above.
Fix
Apply the microsoft sharepoint server security patch or hotfix for CVE-2026-58644 on the affected version, following the vendor advisory for your exact build.
Workarounds
Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.
How to detect CVE-2026-58644
A community-maintained Nuclei template exists for this CVE. You can scan for it directly:
nuclei -id cve-2026-58644 -u https://target- Template
- Microsoft SharePoint Server - WS-Federation BinaryFormatter Deserialization RCE
- Severity
- critical
- Impact
- Unauthenticated attackers can achieve remote code execution as the SharePoint application pool identity (typically a domain service account). This enables full SharePoint farm compromise, machine key extraction for persistent forged authentication tokens, and lateral movement within the domain.
- Remediation
- Apply the July 2026 Cumulative Update (KB5002882 / build 16.0.19725.20434 or later). After patching, rotate farm machine keys using Set-SPMachineKey or Update-SPMachineKey and perform iisreset to revoke any pre-compromise stolen keys. Enable AMSI request-body scanning for /_trust/default.aspx as defense in depth.
Template by ProjectDiscovery nuclei-templates (pdteam), MIT licensed. View the full template. Scan only systems you are authorised to test.
Frequently Asked Questions
Is CVE-2026-58644 being exploited in your environment?
Detect and block the exploit chain at execution, on systems you cannot patch yet.