CVE-2026-21520
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 · uneditedExposure of Sensitive Information to an Unauthorized Actor in Copilot Studio allows a unauthenticated attacker to view sensitive information through network attack vector
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 confidenceCopilot Studio contains an information disclosure vulnerability where an unauthenticated attacker can access sensitive information via network attacks. The vulnerability stems from improper access controls allowing unauthorized visibility into potentially confidential data handled by the Copilot Studio service.
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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Confirm Copilot Studio deploymentIdentify any Microsoft Copilot Studio instances in your environment by reviewing installed services, cloud subscriptions (Azure, Microsoft 365), or web applications matching the Copilot Studio naming convention.Affected if Copilot Studio is deployed in any form in the environment
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Verify network accessibilityDetermine if Copilot Studio endpoints are exposed to the internet or accessible from untrusted networks. Check firewall rules, network security groups, and proxy configurations for inbound access to Copilot Studio URLs.Affected if Copilot Studio is reachable from unauthenticated/untrusted network segments
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Inspect authentication configurationReview Copilot Studio authentication settings through the Microsoft 365 admin center or Azure portal. Verify that guest/external access settings and user consent policies are properly configured.Affected if Authentication allows unauthenticated or guest users to access Copilot Studio resources
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Review access control policiesExamine Copilot Studio tenant-level permissions and sharing policies. Check whether data leak prevention (DLP) policies and conditional access policies are enabled for Copilot Studio workloads.Affected if Least-privilege access controls are not enforced or auditing is disabled
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Audit recent access logsReview Microsoft 365 audit logs, Azure AD sign-in logs, and Copilot Studio usage logs for any unauthorized access attempts or anomalous data access patterns from unfamiliar IP addresses or users.Affected if Logs show access from untrusted sources or unauthenticated requests succeeded
If Copilot Studio is deployed and accessible to unauthenticated users without proper access controls, the environment is affected by this vulnerability.
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 Copilot Studio as they become available. Review and enforce least-privilege access controls and audit authentication configurations for Copilot Studio deployments.
- 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-2026-21520 — 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-2026-21520 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