CVE-2026-20796
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Race Condition in Mattermost 10.11.x Allows Unauthorized Data Access

Publication date: 2026-02-13

Last updated on: 2026-02-23

Assigner: Mattermost, Inc.

Description
Mattermost versions 10.11.x <= 10.11.9 fail to properly validate channel membership at the time of data retrieval which allows a deactivated user to learn team names they should not have access to via a race condition in the /common_teams API endpoint.. Mattermost Advisory ID: MMSA-2025-00549
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Meta Information
Published
2026-02-13
Last Modified
2026-02-23
Generated
2026-06-16
AI Q&A
2026-02-13
EPSS Evaluated
2026-06-14
NVD
CVE-2026-20796
EUVD
EUVD-2026-7378
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
mattermost mattermost_server From 10.11.0 (inc) to 10.11.10 (exc)
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Exploitability
CWE
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KEV
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CWE ID Description
CWE-367 The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.
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Executive Summary

This vulnerability affects Mattermost versions 10.11.x up to and including 10.11.9. It occurs because the software fails to properly validate whether a user is a member of a channel when retrieving data. Specifically, a deactivated user can exploit a race condition in the /common_teams API endpoint to learn the names of teams they should not have access to.

Impact Analysis

The impact of this vulnerability is that a deactivated user may be able to discover team names that they are not authorized to see. Although the vulnerability has a low CVSS base score of 3.1, indicating limited severity, it can lead to unauthorized disclosure of some information about team memberships.

Compliance Impact

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