CVE-2026-6046

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

MEDIUM

5.3

CVSS Score

Published: June 12, 2026 at 03:52 PM UTC

Updated: June 18, 2026 at 02:45 PM UTC

2 products affected across 1 vendorMattermost ServerMattermost

Using Mattermost by Mattermost?

Get instant alerts when new vulnerabilities affect Mattermost - before attackers find them.

Real-time alertsTrack your software stackFree plan available

Start Free Sign In

Severity

MEDIUM5.3

Exploit prediction

EPSS 0.2%

SSVC

No known exploit

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

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Mattermost Server · Mattermost

95%

10.11.0 ≤ v < 10.11.1711.5.0 ≤ v < 11.5.511.6.0 ≤ v < 11.6.2

Affected range stops below 10.11.17, so it looks safe — our inference, not a vendor statement

Affected range stops below 11.5.5, so it looks safe — our inference, not a vendor statement

Affected range stops below 11.6.2, so it looks safe — our inference, not a vendor statement

Mattermost · Mattermost

60%

10.11.0 ≤ v ≤ 10.11.1510.11.0 ≤ v ≤ 10.11.1611.5.0 ≤ v ≤ 11.5.411.6.0 ≤ v ≤ 11.6.110.11.0 11.5.0 11.6.0

Vendor states this is fixed in 10.11.16 (unaffected)

Vendor states this is fixed in 10.11.17 (unaffected)

Vendor states this is fixed in 11.5.5 (unaffected)

Vendor states this is fixed in 11.6.2 (unaffected)

Vendor states this is fixed in 11.7.0 (unaffected)

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

https://mattermost.com/security-updates

References (1)

Vendor Advisory

Source: cverecord

https://mattermost.com/security-updates

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

5.3MEDIUMMattermost

Attack Vector: NETWORK
Complexity: HIGH
Privileges: LOW
User Interaction: NONE
Scope: UNCHANGED
Confidentiality: HIGH
Integrity: NONE
Availability: NONE

Vector?

Quick Info

StatusANALYZED

CWE

CWE-200

Get alerted

Stop reading CVE feeds looking for your own stack

Track the products you run and VulnTracker tells you when a new CVE affects them — with what is known about fixing it, and nothing about the rest.

Create account Sign in

Free plan, no card