Vulnerability report

Active exploitation observed Confirmed confidence In CISA KEV

CVE-2026-58644

Microsoft SharePoint Remote Code Execution Vulnerability

Microsoft SharePoint Enterprise Server 2016 · affected before 16.0.5556.1005

Watch CVE-2026-58644 Browse KEV feed
Severity
CVSS 9.8 · Critical
Confidence
Confirmed
Exploit status
Observed in sensors
EPSS
15.9%
First observed
25 Jul 2026
Last observed
25 Jul 2026

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2026-58644 is an unauthenticated Microsoft SharePoint Remote Code Execution Vulnerability. Deserialization of untrusted data in Microsoft Office SharePoint allows an unauthorized attacker to execute code over a...

Is it exploited?

Yes. Previdian sensors observed exploitation attempts with confirmed confidence. Listed in CISA KEV. Also confirmed by third-party sources.

Who is affected?

Microsoft SharePoint Enterprise Server 2016 affected before 16.0.5556.1005.

What should we do?

Patch immediately, validate internet-facing exposure, and monitor for matching requests.

Overview

Microsoft SharePoint Remote Code Execution Vulnerability

Deserialization of untrusted data in Microsoft Office SharePoint allows an unauthorized attacker to execute code over a network.

Microsoft Affected
Microsoft SharePoint Enterprise Server 2016
Before 16.0.5556.1005
Microsoft Affected
Microsoft SharePoint Server 2019
Before 16.0.10417.20153
Microsoft Affected
Microsoft SharePoint Server Subscription Edition
Before 16.0.19725.20384
View vendor advisory (opens in new tab)
Published
14 Jul 2026
Exploitation Reported
16 Jul 2026
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
None

Tags

microsoft cisa nuclei_scanner

CVE References

Exploitation evidence

Why Previdian marks this CVE as exploited

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploited in the wild

CISA

Recorded 16 Jul 2026

A trusted third party reported exploitation.

Active exploitation observed

Previdian sensor

First observed 25 Jul 2026

Previdian first observed exploitation attempts targeting this vulnerability in our honeypot sensors.

Proof of concept available

Nuclei Templates

Recorded 14 Aug 2026

Public scanner or PoC coverage increases practical exploitability.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the Previdian Pro API.

Learn about Pro API access
Source Added
Microsoft CVRF First 2026-07-14 07:00 UTC
Rapid7 2026-07-14 22:00 UTC
All CISA Advisories 2026-07-16 12:00 UTC
Tenable Blog 2026-07-16 16:00 UTC
CISA 2026-07-16 17:00 UTC
CVE 2026-07-16 17:51 UTC
CERT-EU 2026-07-23 09:13 UTC
Previdian Sensors 2026-07-25 03:20 UTC

Operational indicators for this CVE are listed under Detection.

Sensor telemetry

First-party evidence of exploitation activity

Previdian sensors recorded exploitation attempts targeting this vulnerability. The cards and chart show volume, unique attackers, and daily activity.

1

Attempts observed

1

Unique attacker IPs

1

Attacker countries

HK

1

Sensors observed

CVE-2026-58644 exploitation attempts over the last 83 days

Daily events observed by Previdian sensors

Updated 14 Oct 2026

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24 Jul 10 Aug 27 Aug 13 Sep 14 Oct

First observed 25 Jul 2026 · Last observed 25 Jul 2026

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Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets
User-Agents
Callback hosts
0
0
0

Request targets and User-Agents available in Pro. Callback host details available in Enterprise.

Virtual patch status

No Previdian virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

Learn about virtual patches →

Attacker IP Indicators

Attacker IP indicators observed · available in Pro and Enterprise.

Sensor-derived attacker IP indicators are available to Pro and Enterprise accounts under Detection and through the Pro API.

Learn about Pro API access

Scanner Artifacts

Scanner and exploit-framework references linked to this CVE.

Scanner Reference Detected
Nuclei https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-58644.yaml 14 Aug 2026

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

9.8 Critical

Potential damage if exploited. Separate from whether attackers are using it.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C

EPSS

15.9%

Estimated chance of exploitation in the next 30 days. Previdian's warning comes from evidence, not this score.

Weaknesses

Deserialization of Untrusted Data CWE-502

Recent mention · CERT-EU

2026-009: Critical Vulnerabilities in Microsoft SharePoint

[UPDATED] On 14 July 2026, Microsoft released security updates addressing critical remote code execution (RCE) vulnerabilities in Microsoft SharePoint Server. On 20 July 2026, WatchTowr identified a proof-of-concept exploit code and subsequently observed active exploitation of...

Read full advisory

All Mentions

Recent mention · CERT-EU

2026-009: Critical Vulnerabilities in Microsoft SharePoint

CERT-EU · 23 Jul 2026

[UPDATED] On 14 July 2026, Microsoft released security updates addressing critical remote code execution (RCE) vulnerabilities in Microsoft SharePoint Server. On 20 July 2026, WatchTowr identified a proof-of-concept exploit code and subsequently observed active exploitation of CVE-2026-50522, a vulnerability part of an ongoing series of actively exploited flaws affecting on-premise SharePoint Server instances, including CVE-2026-32201, CVE-2026-45659, CVE-2026-56164, and CVE-2026-58644. CERT-EU strongly recommends updating affected servers immediately, rotating credentials for any assets...

Recent mention · Rapid7

CVE-2026-58644: Microsoft SharePoint Server Unauthenticated Remote Code Execution Vulnerability Exploited in the Wild

Rapid7 · 17 Jul 2026

OverviewOn July 14, 2026, Microsoft published a security advisory addressing CVE-2026-58644, a critical remote code execution (RCE) vulnerability affecting on-premises Microsoft SharePoint Server deployments. The vulnerability, which carries a CVSS v3.1 score of 9.8 (Critical), results from the deserialization of untrusted data (CWE-502) and allows an unauthenticated attacker to execute arbitrary code.Microsoft confirmed active exploitation of CVE-2026-58644, and the vulnerability was subsequently added to CISA’s Known Exploited Vulnerabilities (KEV) catalog on July 16, 2026. In parallel,...

Recent mention · The Hacker News

CISA Adds Exploited SharePoint RCE Zero-Day CVE-2026-58644 to KEV

The Hacker News · 17 Jul 2026

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) on Thursday added a newly patched security flaw impacting Microsoft SharePoint Server to its Known Exploited Vulnerabilities (KEV) catalog, requiring Federal Civilian Executive Branch (FCEB) agencies to apply the fixes by July 19, 2026. The vulnerability in question is CVE-2026-58644 (CVSS score: 9.8), a critical deserialization

Recent mention · Tenable Blog

CVE-2026-32201, CVE-2026-45659, CVE-2026-56164: Frequently Asked Questions About Active Exploitation of Microsoft SharePoint Server Vulnerabilities

Tenable Blog · 16 Jul 2026

Four Microsoft SharePoint Server vulnerabilities are under active exploitation, prompting CISA to issue a hardening alert. An additional high-severity flaw recently patched adds pressure for organizations running on-premises deployments.Key TakeawaysCISA confirmed active exploitation of three on-premises SharePoint Server vulnerabilities (CVE-2026-32201, CVE-2026-45659, CVE-2026-56164), used to gain unauthorized access, establish remote code execution, steal IIS machine keys and deploy malware for persistence.Two additional SharePoint Server vulnerabilities disclosed on July 14, 2026,...

Recent mention · All CISA Advisories

CISA Adds Three Known Exploited Vulnerabilities to Catalog

All CISA Advisories · 16 Jul 2026

CISA has added three new vulnerabilities to its Known Exploited Vulnerabilities (KEV) Catalog, based on evidence of active exploitation. CVE-2026-25089 Fortinet FortiSandbox OS Command Injection Vulnerability   CVE-2026-39808 Fortinet FortiSandbox OS Command Injection Vulnerability   CVE-2026-58644 Microsoft SharePoint Deserialization of Untrusted Data Vulnerability These types of vulnerabilities are frequent attack vectors for malicious cyber actors and pose significant risks to the federal enterprise. Binding Operational Directive (BOD) 26-04: Prioritizing Security Updates Based on Risk...

Recent mention · Rapid7

Patch Tuesday - July 2026

Rapid7 · 14 Jul 2026

Microsoft is publishing 622 vulnerabilities on July 2026 Patch Tuesday, including a record-breaking 416 Windows vulnerabilities. Microsoft is aware of exploitation in the wild for two of the vulnerabilities published today, both of which are listed on CISA KEV, as well as public disclosure for one other. As usual, browser vulns are not included in the Patch Tuesday count above. Rapid7 noted last month that Microsoft no longer enumerates Chromium CVEs in the Security Update Guide. However, Microsoft has now taken the pursuit of minimalism much further, since today’s Security Update Guide no...

Recent mention · All CISA Advisories

CISA Urges SharePoint Hardening After New Exploitations

All CISA Advisories · 14 Jul 2026

CISA is aware of active exploitation of vulnerabilities CVE-2026-32201, CVE-2026-45659, and CVE-2026-56164, enabling cyber threat actors to gain unauthorized access to on-premises SharePoint Server instances. These vulnerabilities affect all supported on-premises SharePoint Server versions (Subscription Edition, 2019, and 2016) and involve establishing remote code execution (RCE) and post-exploitation activities, such as stealing Internet Information Services (IIS) machine keys and performing deserialization techniques, to gain persistence and deploy malware. Organizations should monitor...

Potential Proof of Concepts

These PoCs are unverified and could contain malware. Use at your own risk.

Microsoft SharePoint Server - WS-Federation BinaryFormatter Deserialization RCE

nuclei · Created Unknown

Timeline

From disclosure to observed exploitation

  1. 04:31 UTC

    Public PoC available

    Public proof-of-concept code published

  2. 04:31 UTC

    Nuclei template available

    Scanner coverage available

  3. 03:19 UTC

    Indicator of compromise added

    Indicators of compromise recorded

  4. 03:19 UTC

    Observed by Previdian sensors

    Evidence-backed exploitation signal

  5. 09:13 UTC

    KEV confirmed by CERT-EU

    Exploitation attested by an external source

  6. 17:51 UTC

    KEV confirmed by CVE

    Exploitation attested by an external source

  7. 17:00 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  8. 16:00 UTC

    KEV confirmed by Tenable Blog

    Exploitation attested by an external source

  9. 12:00 UTC

    KEV confirmed by All CISA Advisories

    Exploitation attested by an external source

  10. 22:00 UTC

    KEV confirmed by Rapid7

    Exploitation attested by an external source

  11. 17:05 UTC

    CVE published

    Vulnerability disclosed publicly

  12. 07:00 UTC

    Added to Previdian KEV Feed

    High-confidence, third-party attested exploitation

  13. 21:14 UTC

    CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2026-58644

Free JSON includes basic KEV fields 
{
  "cve_id": "CVE-2026-58644",
  "confidence": "Confirmed",
  "cvss_score": 9.8,
  "cvss_estimated": false,
  "epss_score": 0.15873,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": true
  },
  "sensor_telemetry": { "attempts": 1, "sensors": 1 }
}