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Exchange ServerApplication · Microsoft

CVE-2026-21527

MEDIUM · 6.5 CVSS v3.1 Published 2026-02-10
Fix available
A fix is available. Upgrade to 15.02.2562.037 or later.
See remediation →
74/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

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
User interface (ui) misrepresentation of critical information in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network.

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 · moderate confidence

A UI misrepresentation vulnerability in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing by displaying deceptive or manipulated information in the user interface, potentially tricking users into trusting malicious content or communications that appear legitimate.

MitigationApply Microsoft security updates for Exchange Server when available; implement email authentication controls (SPF, DKIM, DMARC) as defense-in-depth measures to mitigate spoofing attempts.

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
Exchange ServerApplication
Affected:= 2016= 2019
Exchange Server Subscription EditionApplication
Affected:< 15.02.2562.037

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
Low
Integrity
Low
Availability
None

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

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 Exchange Server version via PowerShell
    Run 'Get-ExchangeServer | Select-Object Name, AdminDisplayVersion' in Exchange Management Shell
    Affected if The AdminDisplayVersion shows 2016 or 2019, or for Subscription Edition the build is below 15.02.2562.037
  2. Check exact build number for Subscription Edition
    Run 'Get-ExchangeServer | Format-List Name, BuildVersion' to get the full build version number
    Affected if The BuildVersion is less than 15.02.2562.037 for Subscription Edition
  3. Confirm Exchange Server edition type
    Run 'Get-ExchangeServer | Select-Object Name, Edition' to determine if running Standard or Enterprise edition
    Affected if The server is any 2016 or 2019 edition (Standard or Enterprise) within the affected version range
  4. Review Outlook on the web (OWA) or EAC access logs
    Inspect IIS logs in C:\Program Files\Microsoft\Exchange Server\V15\Logging\OWA or the EAC audit logs for any suspicious UI manipulation attempts
    Affected if Unusual or unexpected UI elements are observed in user sessions (supplementary check)

A user is affected if their Exchange Server version is 2016, 2019, or Subscription Edition with build below 15.02.2562.037, as the UI misrepresentation flaw exists in these unpatched versions.

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
Upgrade available Upgrade to 15.02.2562.037 or later
Fixed in 15.02.2562.037
Interim mitigation

Apply Microsoft security updates for Exchange Server when available; implement email authentication controls (SPF, DKIM, DMARC) as defense-in-depth measures to mitigate spoofing attempts.

Recommended fix Moderate confidence

Exchange Server 2016 CU23+ / Exchange Server 2019 CU14+ / Exchange Server Subscription Edition build 15.02.2562.037 or later

  1. Review the current Exchange Server version by running: Get-ExchangeServer | Format-List Name, Edition, AdminDisplayVersion
  2. For Exchange Server 2016, upgrade to Cumulative Update 23 or later
  3. For Exchange Server 2019, upgrade to Cumulative Update 14 or later
  4. For Exchange Server Subscription Edition, ensure the build version is 15.02.2562.037 or higher
  5. Apply the upgrade in a test environment first to validate compatibility with existing workflows and add-ins
  6. After upgrading, verify that the UI components render correctly and that email spoofing protections are functioning as expected
  7. Review Microsoft documentation for any post-upgrade configuration requirements
Caveat Review release notes for your specific CU version as some legacy protocols or settings may be deprecated; test mail flow and Outlook Web Access thoroughly after upgrade

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

Fix this in Exchange Server Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
Get the upgrade done

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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-2026-21527 in production — separate from our analysis above.

No notes yet

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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