CVE-2026-6046

Plugin bot username conflict allows user account to be used as bot identity in Mattermost Server

Published Jun 12, 2026 CVSS 3.1 · 5.3 Medium EPSS < 1% KEV · Not listed
Description
Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels by pre-registering a user account with a predictable plugin bot username.. Mattermost Advisory ID: MMSA-2026-00649

Remediation

Vendor Solution

Update Mattermost to versions 11.7.0, 11.6.2, 11.5.5, 10.11.16, 10.11.17 or higher.

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-3vmp-whvv-5v9v Mattermost doesn't validate that a username returned during bot registration belongs to a bot account
References
History
Type Values Removed Values Added
First Time appeared Mattermost
Mattermost mattermost
Vendors & Products Mattermost
Mattermost mattermost
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
Description Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels by pre-registering a user account with a predictable plugin bot username.. Mattermost Advisory ID: MMSA-2026-00649
Title Plugin bot username conflict allows user account to be used as bot identity in Mattermost Server
Weaknesses CWE-200
References
Metrics cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
Mattermost
Published
Updated
Jun 12, 2026, 5:18 PM
Reserved
Apr 9, 2026, 7:20 PM
Status
Analyzed
Published
Jun 12, 2026, 5:16 PM
Modified
Jun 18, 2026, 2:33 PM