What is the CVSS score of CVE-2026-6046?

CVE-2026-6046 has a CVSS 3.1 base score of 5.3 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N. EPSS exploitation probability: 0.0%.

Mattermost CVE-2026-6046

EUVD-2026-36502 MEDIUM

Information Exposure (CWE-200)

2026-06-12 Mattermost

GHSA-3vmp-whvv-5v9v

Mattermost Information Disclosure

5.3

CVSS 3.1 · Vendor: Mattermost

Severity by source

Vendor (Mattermost) PRIMARY

5.3 MEDIUM

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

vuln.today AI

5.3 MEDIUM

AC:H reflects required foreknowledge of bot username and pre-registration timing; PR:L for mandatory user account; C:H for full DM interception; no integrity or availability impact.

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

4.0 AV:N/AC:H/AT:P/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (Mattermost).

CVSS VectorVendor: Mattermost

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

Attack Vector

Network

Attack Complexity

High

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

None

Lifecycle Timeline

Analysis Generated

Jun 12, 2026 - 17:35 vuln.today

DescriptionCVE.org

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

AnalysisAI

Private message interception in Mattermost affects versions 11.6.x through 11.6.1, 11.5.x through 11.5.4, and 10.11.x through 10.11.16, allowing a low-privileged attacker to receive plugin-generated direct messages intended for bot accounts. The flaw stems from the bot registration flow failing to verify that a claimed username actually belongs to a bot account, enabling an attacker who pre-registers a human account using a predictable plugin bot username to silently hijack those message channels. No public exploit code exists at time of analysis, and exploitation requires both an existing user account and advance knowledge of the target bot's username.

Technical ContextAI

Mattermost is an open-source team messaging platform with a plugin system that creates bot accounts for automated messaging. During bot registration, the server returns a username but fails to enforce that the returned username maps to a bot-type account (CWE-200: Exposure of Sensitive Information to an Unauthorized Actor). This missing ownership validation in the bot registration API means a regular user account sharing the bot's username will receive direct messages routed by plugins to that username. The affected CPE is cpe:2.3:a:mattermost:mattermost:*:*:*:*:*:*:*:* covering the server component. The root cause is an authorization boundary failure: the system trusts a username string without verifying account type, violating the principle of least privilege at the API layer.

RemediationAI

Patch available per vendor advisory at https://mattermost.com/security-updates (Mattermost Advisory MMSA-2026-00649). Administrators should upgrade to a fixed release beyond the affected version ranges: beyond 11.6.1 for the 11.6.x branch, beyond 11.5.4 for the 11.5.x branch, and beyond 10.11.16 for the 10.11.x branch - exact fix version numbers were not independently confirmed from the provided data. As a compensating control pending upgrade, administrators can audit existing user accounts for usernames that match expected plugin bot naming conventions and remove or rename any suspicious accounts. Additionally, restricting account registration to trusted domains or disabling open user registration limits the attacker's ability to pre-register conflicting usernames. Reviewing plugin bot username patterns to use non-predictable, randomized suffixes can eliminate the predictability prerequisite for exploitation.