CVE-2026-40357
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 · uneditedDeserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code 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 confidenceA deserialization vulnerability in Microsoft Office SharePoint allows an authenticated attacker to execute arbitrary code remotely. The vulnerability stems from unsafe deserialization of data, which can be exploited by sending specially crafted requests to affected SharePoint services.
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< 16.0.19725.20280= 2016= 2019CVSS 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
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:L/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 checksWork through these to decide whether this CVE applies to you.
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Check SharePoint Server versionOpen SharePoint Management Shell and run: (Get-SPFarm).BuildVersion or check Central Administration > System Settings > Manage server in this farmAffected if Version is 16.0.19725.20280 or higher (not affected); version is below 16.0.19725.20280, or version matches 2016 or 2019 releases (affected)
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Confirm SharePoint edition and releaseRun: Get-SPServer -Farm | Select-Object -First 1 | ForEach-Object { $_.Farm.BuildVersion }; Also check registry at HKLM\SOFTWARE\Microsoft\Shared Tools\Web Server Extensions\16.0\SharePoint\Setup\Version for installation detailsAffected if Server is SharePoint Server 2016 or 2019 (any build) - these are explicitly listed as affected versions
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Verify SharePoint services are runningIn SharePoint Management Shell run: Get-Service | Where-Object {$_.Name -like '*SP*' -and $_.Status -eq 'Running'} to confirm SharePoint services are activeAffected if SharePoint services are running - the deserialization flaw exists in these services and can be triggered by authenticated requests
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Check if SharePoint is exposed to untrusted networksReview firewall rules and load balancer configuration to determine if SharePoint sites are accessible from the internet or untrusted internal networksAffected if SharePoint is externally accessible - an unauthenticated attacker would first need valid credentials, but external exposure increases attack surface
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Audit SharePoint user accountsIn Central Administration > Security > Manage users, review all user accounts. In SharePoint Management Shell run: Get-SPUser to list users. Check for any unauthorized or unexpected accountsAffected if There are user accounts beyond expected administrators - the attacker needs valid authentication to exploit the deserialization flaw
You are affected if your SharePoint Server version is below 16.0.19725.20280, or if you are running SharePoint Server 2016 or 2019 (any build), and the server has user accounts configured for authentication.
Generated from the published advisory. Verify against your own configuration.
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 · scoped16.0.19725.20280
Apply Microsoft security patches for SharePoint immediately upon release. Prioritize testing in a non-production environment to verify compatibility before deploying the fix across production SharePoint farms.
SharePoint Server 2016/2019: Upgrade to version 16.0.19725.20280 or later (November 2024 security updates)
- Identify the current SharePoint Server version by navigating to Central Administration > System Settings > Manage farm configuration
- For SharePoint Server 2016: Install the November 2024 security update (KB5002566) or later which includes the fix version 16.0.19725.20280
- For SharePoint Server 2019: Install the November 2024 security update (KB5002571) or later which includes the fix version 16.0.19725.20280
- Download and apply the update from the Microsoft Update Catalog or through Windows Update/WSUS
- After installation, verify the farm version shows 16.0.19725.20280 or higher in Central Administration > System Settings > Manage farm configuration
- Test critical SharePoint workflows post-update to ensure functionality
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation8.0 h
- Implementation16.0 h
- Testing24.0 h
- Review / QA12.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $16,384.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-40357 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-40357 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- 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