CVE-2026-6046 — Plugin bot username conflict allows user account to be used as bot identity in Mattermost Server

Description (CNA)

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

Affected (CNA)

Vendor / product	Versions
Mattermost / Mattermost	affected 11.6.0 through 11.6.1; affected 11.5.0 through 11.5.4; affected 10.11.0 through 10.11.15; affected 10.11.0 through 10.11.16; unaffected 11.7.0; unaffected 11.6.2; unaffected 11.5.5; unaffected 10.11.16; unaffected 10.11.17

CWE

CWE-200

References

https://mattermost.com/security-updates

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.