CVE-2026-6046

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

CVSS 5.3 MEDIUMEPSS 0.2%CWE-200

Vexday Risk Score

13Low

SSVC decision (CISA)

Track

No exploitation signal → monitor

CVSS 5.3EPSS 0.2%KEV nãoPoC —Nuclei —Metasploit —Patch referenciado

Lifecycle

12 Jun 2026Published on NVD

Recommendation: Monitor — no exploitation signal at the moment.

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

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N

Affected products

Mattermost · Mattermost

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References

https://mattermost.com/security-updates