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cve recordcriticalexploited in the wildzero day3 of 3 cataloguesexploit reported

CVE-2026-58644

Microsoft · SharePoint · Microsoft SharePoint Deserialization of Untrusted Data Vulnerability

Published · Added to CISA KEV
CVSS9.8
Severitycritical
WeaknessCWE-502
EPSS15.9%96.9th percentile
Exploited3 KEV sources
Ransomware useUnknown
Federal fix dueJul 19, 2026

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

patch window

Called exploited the same day it was disclosed.

Measured from the CVE publication date to the earliest of 3 KEV catalogues that list it.

The life of this vulnerability

  1. CVE published
  2. First KEV listingsame day
  3. Last KEV listing2d
  4. Last sighting35d

Gaps are compressed to equal steps. The elapsed time is printed under each.

Which catalogues call it exploited

Sources3 of 3
Listings differ by2 d
Strongest claimconfirmed

3 catalogues list it. CIRCL aggregates the others and is shown but not counted.

Public exploitation evidence

8 public reports collected from VulnCheck and CIRCL, first on Jul 14, 2026. Each links to its original source. We have not verified them.

Description

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

Required action (CISA)

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.

References

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Our coverage of CVE-2026-58644

CVE-2026-55040critical

Attackers Exploit SharePoint Authentication Bypass After Public PoC Release

Threat actors are actively exploiting a critical Microsoft SharePoint vulnerability, identified as CVE-2026-55040, according to recent reports. This exploitation campaign began shortly after a proof-of-concept (PoC) exploit for the flaw was publicly released. The vulnerability is described as a security feature bypass, enabling unauthenticated attackers to impersonate legitimate users within…

CVE-2008-4128high

July 2026 CVE Landscape

Cybersecurity researchers identified 85 high-impact vulnerabilities in July 2026 that require urgent remediation, marking a 44% increase from the previous month. Of these, 36 were assigned a "Very Critical" risk score by Insikt Group. The vulnerabilities affected products from 61 vendors, with Microsoft accounting for approximately 12% of the total.

CVE-2026-25089critical

CISA Adds Fortinet and Microsoft Flaws to Exploited Vulnerabilities List

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) has added three new vulnerabilities to its Known Exploited Vulnerabilities (KEV) catalog, requiring federal agencies to address them by July 19, 2026. The newly listed flaws include one affecting Microsoft SharePoint and two impacting Fortinet FortiSandbox products.

CVE-2026-58644critical

Microsoft SharePoint Server RCE Vulnerability Exploited in the Wild

Microsoft has confirmed active exploitation of a critical remote code execution (RCE) vulnerability, CVE-2026-58644, affecting on-premises deployments of its SharePoint Server. The vulnerability, which stems from the deserialization of untrusted data (CWE-502), allows an unauthenticated attacker to execute arbitrary code with a CVSS v3.1 score of 9.8 (Critical).