CVE-2026-2458
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Improper Access Control in Mattermost Allows Channel Enumeration

Publication date: 2026-03-16

Last updated on: 2026-03-18

Assigner: Mattermost, Inc.

Description
Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to properly validate team membership when searching channels which allows a removed team member to enumerate all public channels within a private team via the channel search API endpoint.. Mattermost Advisory ID: MMSA-2025-00568
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Meta Information
Published
2026-03-16
Last Modified
2026-03-18
Generated
2026-06-16
AI Q&A
2026-03-16
EPSS Evaluated
2026-06-15
NVD
CVE-2026-2458
EUVD
EUVD-2026-12409
Affected Vendors & Products
Showing 3 associated CPEs
Vendor Product Version / Range
mattermost mattermost_server From 10.11.0 (inc) to 10.11.11 (exc)
mattermost mattermost_server From 11.2.0 (inc) to 11.2.3 (exc)
mattermost mattermost_server From 11.3.0 (inc) to 11.3.1 (exc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-862 The product does not perform an authorization check when an actor attempts to access a resource or perform an action.
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Executive Summary

This vulnerability exists in certain versions of Mattermost (11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10) where the system fails to properly validate team membership during channel searches.

Because of this improper validation, a user who has been removed from a private team can still enumerate all public channels within that private team by using the channel search API endpoint.

Impact Analysis

The impact of this vulnerability is that a removed team member can gain information about public channels inside a private team that they should no longer have access to.

This could lead to unauthorized disclosure of information about team structure or channel existence, potentially aiding further reconnaissance or social engineering attacks.

The CVSS base score of 4.3 indicates a low to medium severity impact, specifically limited to confidentiality (partial information disclosure) without affecting integrity or availability.

Compliance Impact

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