# Microsoft Teams Third-Party App Security: What to Review Before Granting Access

> Third-party apps in Microsoft Teams can request broad access to your Teams data. The security review to run before granting access, and how to govern Teams apps across the organisation.

Source: https://playciso.com/blog/microsoft-teams-third-party-app-security · Published: 2026-09-26 · Publisher: PlayCISO (https://playciso.com)

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"What security review does a third-party tool need before we grant it access to our Teams data?" is a question every organisation using Microsoft Teams eventually faces — often after someone has already one-click-installed an app that requested access to every message and file. Teams apps run inside your collaboration platform, so granting one access is a real third-party data-access decision. ## Why Teams apps are a risk Third-party apps and integrations can request access to messages, files, channels and user data. An over-permissioned app can read or exfiltrate sensitive conversations and documents; a poorly-secured or malicious one becomes a path to that data. The one-click install can quietly bypass the vendor-risk scrutiny the same access would get anywhere else. ## The review to run before granting access - Permissions vs need: does it request only what its function requires? A narrowly-useful app wanting sweeping access is a red flag. - Publisher reputation: is it a verified/publisher-attested app from a reputable vendor? - Data flow: where does your data go, and how is it stored and handled? - Governance fit: does it meet your privacy, data-residency and compliance requirements? ## Govern apps across the organisation Do not rely on individual users. Use Teams admin controls to maintain an **allowlist** of approved apps and block the rest, **restrict who can add apps**, **require review** before approving a new one, and **re-review periodically**. This is least-privilege and vendor-risk discipline applied at scale. Run a structured third-party review with the free [Vendor Risk tool →](/tools/vendor-risk), see the wider hardening steps in [Microsoft Teams security best practices](/blog/microsoft-teams-security-best-practices), and govern agent/tool access with [MCP Guard](/tools/mcpguard). ## Frequently asked questions **What review does a Teams app need?** Permissions vs need, publisher reputation/verification, data flow, and governance/compliance fit. **Why are Teams apps risky?** They run inside your platform and can access messages/files/data; one-click install can bypass vendor scrutiny. **How to govern at scale?** Allowlist approved apps, restrict who can add them, require review, and re-review periodically. **Which permissions concern?** Broad read-all-messages / all-files / tenant-wide access that exceeds the app's purpose.