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How the CVE Works
The vulnerability exists in the MSTeams plugin’s OAuth authorization flow. When a user authenticates via Microsoft Teams, the plugin generates a redirect URL with parameters identifying the post to be updated. Mattermost versions 10.11.3 and earlier fail to validate that the post ID embedded in the incoming OAuth request truly belongs to the user initiating the request. An attacker can craft a malicious OAuth redirect URL containing the identifier of any arbitrary post on the server. When this crafted URL is processed by the vulnerable Mattermost instance, the system incorrectly associates the authenticated user’s session with the target post, allowing the attacker to edit or potentially delete content they do not own, leading to a complete compromise of post integrity.
Platform: Mattermost
Version: <=10.11.3
Vulnerability: Access Control
Severity: Critical
date: 11/14/2025
Prediction: Patch by 12/15/2025
What Undercode Say:
`curl -X POST http://
`git log –grep=”MSTeams” –oneline`
`grep -r “msteams.oauth” apps/`
How Exploit:
Craft a state parameter in the OAuth callback to reference an unauthorized post ID.
Protection from this CVE
Upgrade Mattermost immediately.
Disable MSTeams plugin.
Implement post-ID validation.
Impact:
Arbitrary post modification
Data integrity loss
Privilege escalation
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Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
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