CVE-2026-45659

Microsoft SharePoint Server: Deserialization of Untrusted Data

As of , CVE-2026-45659 in Microsoft SharePoint Server is on CISA's list of exploited vulnerabilities: CISA listed it on . Our patch-first group: Patch now.

Exploited
Yes: CISA listed it on 1 July 2026
US federal deadline
4 July 20263 days after CISA listed it. US federal civilian agencies must fix it by then.
Used in ransomware campaigns
KnownCISA changed it from Unknown to Known on 10 August 2026.
Forensic triage
Required by CISA under BOD 26-04Agencies must also look for signs that attackers already got in.
EPSS score
0.03Higher than 85% of the CVEs EPSS scores. EPSS estimates the chance of exploitation activity in the next 30 days.
Public exploit
None foundNeither Metasploit nor Exploit-DB lists one.
Fix
Vendor advice: msrc.microsoft.comLinks below, from CISA's entry.

What CISA says to do

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.

CISA's required action

What the flaw is

Microsoft SharePoint Server contains a deserialization of untrusted data vulnerability which allows an authorized attacker to execute code over a network.

CISA's description

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

The CVE record's description, from microsoft

CVE published
22 May 2026
Assigned by
microsoft
CVSS
8.8 High (CVSS 3.1, from the CNA)
CWE-502
Deserialization of Untrusted Data
CISA SSVC, exploitation
active
CISA SSVC, automatable
no
CISA SSVC, technical impact
total

Timeline

  1. The CVE record was published.
  2. CISA added it to its list of exploited vulnerabilities.
  3. The US federal deadline to fix it.
  4. CISA changed its entry. Ransomware use: Unknown to Known.

SharePoint Server: other exploited entries

VulnerabilityProductOur groupListedDeadlineEPSS
CVE-2026-56164Missing Authentication for Critical FunctionMicrosoft SharePoint ServerPatch nowForensic triage required by CISA0.01
CVE-2023-24955Code InjectionMicrosoft SharePoint ServerPatch this weekRansomware use; Metasploit module; EPSS 0.850.85
CVE-2023-29357Privilege EscalationMicrosoft SharePoint ServerPatch this weekRansomware use; Metasploit module; EPSS 0.990.99
CVE-2026-32201Improper Input ValidationMicrosoft SharePoint ServerPatch soon0.43

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