CVE-2026-21535
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 · uneditedImproper access control in Microsoft Teams allows an unauthorized attacker to disclose information 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 confidenceThis vulnerability in Microsoft Teams involves improper access control that allows unauthorized attackers to potentially disclose sensitive information over a network. The flaw appears to enable access to resources or data without proper authentication or authorization checks, which could expose conversations, files, or other Teams data to unauthorized parties.
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 dataall versionsCVSS 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
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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 checksWork through these to decide whether this CVE applies to you.
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Identify installed Microsoft Teams versionOpen Teams, click your profile picture > About > About Microsoft Teams. Alternatively, check Programs and Features or run 'Get-ItemProperty -Path "HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\MSTeams" | Select-Object DisplayVersion' in PowerShellAffected if Any version of Teams is installed (all versions are affected)
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Verify guest/external access settingsIn Teams admin center, go to Users > Guest access, or check org-wide settings > External access. For desktop client, check File > Manage account > GuestAffected if Guest access or external access is enabled without strict controls
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Review Teams sharing policiesIn Teams admin center, navigate to Teams > Teams policies > Sharing policies. Check if external file sharing is set to 'Anyone' or permissive sharing is enabledAffected if Permissive sharing policies allow external users to access files or data without restrictions
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Check for anonymous join links or public sharingReview scheduled meetings and channels for anonymous/guest join links. Check SharePoint/OneDrive sharing settings integrated with TeamsAffected if Public or anonymous access links exist for Teams meetings or channel content
If Microsoft Teams is running with guest/external access enabled or permissive sharing policies, the environment may be vulnerable to unauthorized information disclosure via this improper access control flaw.
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.
From vendor dataApply Microsoft security patches for Teams when available, and review Teams sharing settings and guest access configurations to limit exposure. Consider network segmentation to restrict Teams traffic to trusted networks.
- Consultation2.0 h
- Implementation1.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-21535 — 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-2026-21535 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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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.
- 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