CVE-2026-3433

Analyzed Analyzed - Analysis Complete

Information Disclosure in Mattermost via WebSocket Events

Publication date: 2026-06-12

Last updated on: 2026-06-18

Assigner: Mattermost, Inc.

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 restrict role_updated websocket event broadcasts to members of the affected team or channel which allows an authenticated attacker with guest-level access to observe permission scheme change notifications for private teams they are not a member of via the websocket connection.. Mattermost Advisory ID: MMSA-2026-00616

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-06-12

Last Modified

2026-06-18

Generated

2026-07-03

AI Q&A

2026-06-12

EPSS Evaluated

2026-07-01

NVD

CVE-2026-3433

EUVD

EUVD-2026-36498

Affected Vendors & Products

Vendor	Product	Version / Range
mattermost	mattermost_server	From 10.11.0 (inc) to 10.11.17 (exc)
mattermost	mattermost_server	From 11.5.0 (inc) to 11.5.5 (exc)
mattermost	mattermost_server	From 11.6.0 (inc) to 11.6.2 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-200	The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.

Attack-Flow Graph

Mitigation Strategies

To mitigate this vulnerability, you should upgrade Mattermost to a version later than the affected versions: 11.6.1, 11.5.4, or 10.11.16.

This vulnerability allows an authenticated attacker with guest-level access to observe permission scheme change notifications for private teams they are not a member of via the websocket connection. Upgrading to a fixed version will restrict role_updated websocket event broadcasts properly.

For more information and updates, refer to Mattermost's official security updates page.

Compliance Impact

This vulnerability allows an authenticated attacker with guest-level access to observe permission scheme change notifications for private teams they are not a member of via the websocket connection.

Such unauthorized access to permission change information could potentially lead to exposure of sensitive information or unauthorized insight into internal team structures.

However, there is no explicit information provided about the direct impact of this vulnerability on compliance with common standards and regulations like GDPR or HIPAA.

Impact Analysis

The impact of this vulnerability is that an attacker with guest-level access can gain unauthorized visibility into permission scheme change notifications for private teams they do not belong to.

This could lead to information disclosure about internal permission changes within private teams, potentially aiding further attacks or unauthorized access attempts.

Executive Summary

This vulnerability exists in certain versions of Mattermost (11.6.x <= 11.6.1, 11.5.x <= 11.5.4, and 10.11.x <= 10.11.16) where the system fails to restrict the broadcasting of role_updated websocket events to only members of the affected team or channel.

As a result, an authenticated attacker with guest-level access can observe permission scheme change notifications for private teams they are not a member of via the websocket connection.

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