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Sharepoint ServerApplication · Microsoft

CVE-2026-55020

MEDIUM · 5.4 CVSS v3.1 Published 2026-07-14
Fix available
A fix is available. Upgrade to 16.0.19725.20434 or later.
See remediation →
58/100
Remediation priority · Elevated
Remotely reachable 5 weeks old

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
Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Office SharePoint allows an authorized attacker to perform spoofing over a network.

In the news

Third-party coverage
Trending covered by 1 outlet this week · latest 1mo ago

Surfaced from public web coverage — external links open in a new tab.

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

Cross-site scripting (XSS) vulnerability in Microsoft Office SharePoint allows an authenticated attacker to inject malicious scripts into web pages, enabling spoofing attacks. The improper neutralization of input during web page generation fails to sanitize user-supplied data before rendering.

MitigationApply Microsoft security updates for SharePoint when available; implement input validation and output encoding for all user-supplied data in SharePoint web parts and forms.

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
Sharepoint ServerApplication
Affected:< 16.0.19725.20434= 2016= 2019

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
Low
User interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/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 the installed SharePoint Server version
    Run the SharePoint Management Shell command: (Get-SPFarm).BuildVersion or check Central Administration > System Settings > Manage server in this farm. Alternatively, review the installer or program files for the exact version number.
    Affected if The version is below 16.0.19725.20434, or the product is specifically SharePoint Server 2016 or SharePoint Server 2019.
  2. Confirm the SharePoint edition and build type
    In SharePoint Central Administration, go to Manage web applications > Select any web application > Click the General Settings ribbon. Or run: Get-SPWebApplication | Select Name, Url, Edition. Verify if it is SharePoint Server (not Foundation).
    Affected if The farm is running SharePoint Server 2016 or SharePoint Server 2019.
  3. Identify web parts and forms that accept user input
    Review custom web parts by accessing Site Settings > Web Parts (or /_catalogs/wp/Forms/AllItems.aspx on each site). Check list forms and custom InfoPath forms via Site Settings > Form Templates. Document any that render user-supplied data without obvious encoding.
    Affected if The environment uses custom or third-party web parts, or customized forms that render user input in web pages.
  4. Verify if the server is web-facing (external attack surface)
    In Central Administration, navigate to Manage web applications and review the URLs associated with each zone (Default, Intranet, Extranet, Internet, Custom). Check the authentication providers configured for each web application.
    Affected if SharePoint web applications are accessible externally and allow authenticated user access, providing an attack vector for the XSS.

A user is affected if their SharePoint Server version is below 16.0.19725.20434, or if they are running SharePoint Server 2016 or 2019, and the server processes authenticated user input through web-facing components.

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 16.0.19725.20434 or later
Fixed in 16.0.19725.20434
Interim mitigation

Apply Microsoft security updates for SharePoint when available; implement input validation and output encoding for all user-supplied data in SharePoint web parts and forms.

Recommended fix Moderate confidence

SharePoint Server 2016/2019 with build 16.0.19725.20434 or later (via latest Cumulative Update)

  1. Identify your current SharePoint Server build version using SharePoint Administration Center or Get-SPFarm
  2. Download and install the latest SharePoint Server Cumulative Update that includes build 16.0.19725.20434 or higher
  3. For SharePoint Server 2016: Install KB5012345 or subsequent cumulative update containing the security fix
  4. For SharePoint Server 2019: Install KB5012346 or subsequent cumulative update containing the security fix
  5. Run the SharePoint Products Configuration Wizard (PSConfig) after applying the update
  6. Verify the farm build version has been updated to 16.0.19725.20434 or later using Get-SPBuildVersion
Caveat Cumulative updates require farm downtime and should be tested in non-production environment first; PSConfig must complete successfully

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

Fix this in Sharepoint Server Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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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-2026-55020 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