dbcve.org
Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 4 Apr 2023.
365 AppsApplication · Microsoft

CVE-2023-23397

CRITICAL · 9.8 CVSS v3.1 Published 2023-03-14
Patch available
A vendor patch is available. No clean upgrade release — apply the published patch.
See remediation →
100/100
Remediation priority · Urgent
In the wild High EPSS Remotely reachable No privileges Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Microsoft Outlook Elevation of Privilege Vulnerability

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

This is an elevation of privilege vulnerability in Microsoft Outlook for Windows where specially crafted emails containing UNC paths can trigger automatic NTLM authentication to an attacker-controlled server. This allows credential theft (NTLM relay) and enables the attacker to impersonate the victim user without interaction.

MitigationApply the Microsoft security update (March 2023) to all affected Outlook clients. Additionally, block outbound SMB (ports 445/139) at network perimeter and enable Extended Protection for Authentication in Exchange Server.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
365 AppsApplication
Affected:all versions
OfficeApplication
Affected:= 2019
Office Long Term Servicing ChannelApplication
Affected:= 2021
OutlookApplication
Affected:= 2013= 2016

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed Outlook version
    Open Outlook, go to File > Office Account > About Outlook, or check Programs and Features for Microsoft Outlook entry
    Affected if Version is 2013, 2016, 2019, or 2021, or if using Microsoft 365 Apps
  2. Check Windows version for patch status
    Run 'winver' command or check System Properties to confirm Windows version, then verify if KB5002537 or later updates are installed via Windows Update history
    Affected if Outlook is unpatched and KB5002537 or subsequent Outlook security updates are not installed
  3. Verify NTLM authentication settings
    Check registry key HKLM\SYSTEM\CurrentControlSet\Control\Lsa for 'LmCompatibilityLevel' setting, or examine Outlook security settings in Trust Center
    Affected if NTLM authentication is enabled without restriction or Outlook does not have enhanced protection configured
  4. Confirm Outlook account configuration
    Review configured email accounts in Outlook via File > Account Settings > Account Settings, noting if any connect to on-premises Exchange or use basic authentication
    Affected if Accounts use legacy authentication protocols without modern authentication (OAuth) enforcement

You are affected if your Outlook version matches 2013, 2016, 2019, 2021, or Microsoft 365 Apps, and security updates after March 2023 are not installed.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Patch available Apply the vendor patch
Vendor patch msrc.microsoft.com →
Interim mitigation

Apply the Microsoft security update (March 2023) to all affected Outlook clients. Additionally, block outbound SMB (ports 445/139) at network perimeter and enable Extended Protection for Authentication in Exchange Server.

Recommended fix High confidence

Microsoft 365 apps: March 2023 monthly channel or later; Outlook 2016: version 16.0.15330.20000 or later with March 2023 security update; Outlook 2013: March 2023 security update (KB5002537)

  1. Verify the current Microsoft Outlook version by opening Outlook, going to File > Office Account > About Outlook
  2. For Microsoft 365/Office 365 subscriptions: Ensure automatic updates are enabled or manually check for updates via File > Office Account > Update Options > Update Now
  3. For Outlook 2016: Install the March 2023 security update (KB5002537) or later from Microsoft Update Catalog
  4. For Outlook 2013: Install the March 2023 security update (KB5002537) from Microsoft Update Catalog
  5. After updating, verify the version includes the March 2023 security patch by checking Help > About Microsoft Outlook
Caveat No major breaking changes; March 2023 security update is a routine patch

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in 365 Apps Exploited in the wild — priority engagement
  • Consultation8.0 h
  • Implementation16.0 h
  • Testing8.0 h
  • Review / QA4.0 h
36.0 hours of engineering $6,400
Get it fixed fast

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $10,240.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2023-23397 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2023-23397 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data