CVE-2026-6046CWE-200

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

Medium · published June 12, 2026

CVSS v3.1
5.3
EPSS
0%
Percentile
21.9
In the wild
Unconfirmed
What it is

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

The record
Technical detail
CVSS v3.1
5.3 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
CVSS v4.0
Not supplied
EPSS
0.00303 · 21.9th percentile
Weakness
CWE-200 · Exposure of Sensitive Information to an Unauthorized Actor
Published
2026-06-12T15:52Z
EPSS history
Timeline
  • 12 JUN 15:52Z
    Plugin bot username conflict allows user account to be used as bot identity in Mattermost Server
    cvelistv5