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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

PUBLISHED Reserved 2026-04-09 | Published 2026-06-12 | Updated 2026-06-12 | Assigner Mattermost




MEDIUM: 5.3CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N

Problem types

CWE-200 Exposure of Sensitive Information to an Unauthorized Actor

Product status

Default status
unaffected

11.6.0 (semver)
affected

11.5.0 (semver)
affected

10.11.0 (semver)
affected

10.11.0 (semver)
affected

11.7.0
unaffected

11.6.2
unaffected

11.5.5
unaffected

10.11.16
unaffected

10.11.17
unaffected

Credits

insomnia1102 finder

References

mattermost.com/security-updates (MMSA-2026-00649) vendor-advisory

cve.org (CVE-2026-6046)

nvd.nist.gov (CVE-2026-6046)

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