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Vulnerability · Published Mar 16, 2026 · Assigned by Mattermost

CVE-2026-2458Unauthorized channel enumeration in private teams after member removal

Medium 4.3

In plain English

A medium-severity missing authorization in Mattermost from Mattermost. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 7% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)4.3Medium
Exploit odds (30 days)0.2%top 93.4% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official 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

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Gogithub.com/mattermost/mattermost-server11.2.3GHSA-679f-wmrg-qf57
Gogithub.com/mattermost/mattermost-server5.3.2-0.20260113182106-a18b80ba4c32GHSA-679f-wmrg-qf57
Gogithub.com/mattermost/mattermost-server10.11.11GHSA-679f-wmrg-qf57
Gogithub.com/mattermost/mattermost-server11.3.1GHSA-679f-wmrg-qf57
Gogithub.com/mattermost/mattermost-server10.11.11+incompatible, 11.2.3+incompatible, 11.3.1+incompatibleGO-2026-4729
Gogithub.com/mattermost/mattermost-server/v5no fix listedGO-2026-4729
Gogithub.com/mattermost/mattermost-server/v6no fix listedGO-2026-4729
Gogithub.com/mattermost/mattermost/server/v88.0.0-20260113182106-a18b80ba4c32GO-2026-4729
Gogithub.com/mattermost/mattermost/server/v88.0.0-20260113182106-a18b80ba4c32GHSA-679f-wmrg-qf57

Affected products (as reported)

VendorProductVersions
Mattermost Mattermost 11.3.0 – through 11.3.011.2.0 – through 11.2.210.11.0 – through 10.11.10

Weakness: CWE-862 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

References