IRONSMITHINTEL
HIGHCVSS8.8
|
Actively Exploited
|CISA KEV|CVE-2023-35311|Auth: none — unauthenticated|Reboot: required|Manual only

KB5002427: Windows Server Security Update (July 2023)

Microsoft Outlook contains a security feature bypass vulnerability that allows an attacker to bypass the Microsoft Outlook Security Notice prompt.

Published Jul 11, 2023 · Updated May 16, 2026
Why patchRisk explained in plain English
Worst-case scenarioIf unpatched

A remote attacker, without authentication, can achieve full data confidentiality loss, arbitrary modification of data, complete denial of service or system unavailability. Federal agencies are required to remediate by 2023-08-01 under CISA BOD 22-01.

How the attack worksNo clicks needed

This is a Software Vulnerability (CWE-367) (CWE-367) vulnerability in Microsoft Outlook. Exploitation requires remote network access, low attack complexity, no authentication required, and user interaction required.

📧

Phishing link

→

🖼

Malicious file

🔓

Server compromised

Am I affected?Quick check

Probably yes if any of these apply:

●Exchange Administrators
●Messaging Team
●IT Security
●Running 365 apps: -; office: 2019; office long term servicing channel: 2021; outlook: 2013, 2016
Fixed inKB5002427, KB5002432, KB5029827 (applies to 11 product versions) — build 15.0.5571.1000, 16.0.5404.1000+
Real-world incidentsWhat we've seen

CISA added this CVE to the Known Exploited Vulnerabilities catalog on 2023-07-11 based on evidence of active exploitation in the wild. Federal agencies required to remediate by 2023-08-01.

How to patch

Manual download

For air-gapped servers or out-of-band deployment. Microsoft Update Catalog returns every OS-version variant of this update.

↗ Microsoft Update CatalogKB5002427

Manual remediation steps

Apply the Microsoft Security Update

Microsoft has released an official security update that fixes this vulnerability.

Required KB Updates

    1
    KB5002427 — https://support.microsoft.com/help/5002427
    1
    KB5002432 — https://support.microsoft.com/help/5002432
    1
    KB5029827 — https://support.microsoft.com/help/5029827

Supersedes: KB5002382, KB5002387

Affected Products

    1
    Microsoft 365 Apps for Enterprise for 32-bit Systems
    1
    Microsoft 365 Apps for Enterprise for 64-bit Systems
    1
    Microsoft Office 2019 for 32-bit editions
    1
    Microsoft Office 2019 for 64-bit editions
    1
    Microsoft Office LTSC 2021 for 32-bit editions
    1
    Microsoft Office LTSC 2021 for 64-bit editions
    1
    Microsoft Outlook 2013 (32-bit editions)
    1
    Microsoft Outlook 2013 (64-bit editions)
    1
    Microsoft Outlook 2013 RT Service Pack 1
    1
    Microsoft Outlook 2016 (32-bit edition)
    1
    Microsoft Outlook 2016 (64-bit edition)

Fixed Build Numbers

    1
    15.0.5571.1000
    1
    16.0.5404.1000
    1
    https://aka.ms/OfficeSecurityReleases

Installation Methods

Windows Update (recommended)

1
Settings → Windows Update → Check for updates
2
The security update is offered if your system is in scope
3
Restart when prompted (may or may not be required for this update)

Microsoft Update Catalog (manual download)

1
Open https://catalog.update.microsoft.com
2
Search for KB5002427
3
Download the package matching your OS architecture and Windows build
4
Run the .msu installer with administrator privileges
5
Restart when prompted

WSUS / SCCM / Intune

Approve KB5002427 for the affected products in your update management console.

Microsoft Download Center Links

    1
    https://www.microsoft.com/download/details.aspx?familyid=168ce814-7e8d-499c-ab3d-2dbaad8c2f10
    1
    https://www.microsoft.com/download/details.aspx?familyid=91d8c005-a747-4a7d-906d-bb046ef85020
    1
    https://www.microsoft.com/download/details.aspx?familyid=d1a6716a-9986-4e16-aadb-0825ffdb28e1
    1
    https://www.microsoft.com/download/details.aspx?familyid=dcb65391-061a-4dc2-ae06-83ed610f7f81

Verification

Confirm the update is installed:

Get-HotFix | Where-Object { $_.HotFixID -in @('KB5002427','KB5002432','KB5029827') }

References

    1
    Microsoft Security Response Center: https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2023-35311
    1
    KB article: https://support.microsoft.com/help/5029827
    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2023-35311
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-35311

Discovery Credit

Anonymous

PowerShell automationComing soon

No tested PowerShell script for this entry yet. We’re prioritising automation based on user demand.

References

↗ CVE-2023-35311↗ MSRC Advisory↗ NVD↗ KBKB5002427