CVE-2026-9162

Analyzed Analyzed - Analysis Complete

Authentication Bypass in Mattermost via Cached WebSocket Sessions

Publication date: 2026-06-22

Last updated on: 2026-06-23

Assigner: Mattermost, Inc.

Description

Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17 fail to invalidate cached authentication state for active WebSocket connections during global session revocation, which allows a user with an existing WebSocket connection to remain authenticated and continue receiving real-time events until the cached session expires or the client reconnects.. Mattermost Advisory ID: MMSA-2026-00664

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published

2026-06-22

Last Modified

2026-06-23

Generated

2026-07-12

AI Q&A

2026-06-22

EPSS Evaluated

2026-07-11

NVD

CVE-2026-9162

EUVD

EUVD-2026-38247

Affected Vendors & Products

Vendor	Product	Version / Range
mattermost	mattermost_server	From 10.11.0 (inc) to 10.11.18 (exc)
mattermost	mattermost_server	From 11.7.0 (inc) to 11.7.1 (exc)
mattermost	mattermost_server	From 11.5.0 (inc) to 11.5.6 (exc)
mattermost	mattermost_server	From 11.6.0 (inc) to 11.6.3 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-613	According to WASC, "Insufficient Session Expiration is when a web site permits an attacker to reuse old session credentials or session IDs for authorization."

Attack-Flow Graph

Executive Summary

This vulnerability affects certain versions of Mattermost where the system fails to invalidate cached authentication states for active WebSocket connections during a global session revocation.

As a result, a user who already has an active WebSocket connection can remain authenticated and continue to receive real-time events even after their session has been revoked, until the cached session expires or the client reconnects.

Impact Analysis

The impact of this vulnerability is that a user with an active WebSocket connection may continue to have access to real-time data and events despite their session being globally revoked.

This could lead to unauthorized access to information or continued interaction with the system beyond the intended session lifetime.

According to the CVSS score, the impact on confidentiality is low, with no impact on integrity or availability.

Mitigation Strategies

To mitigate this vulnerability, you should upgrade Mattermost to a version later than the affected versions: 11.7.0, 11.6.2, 11.5.5, or 10.11.17.

Since the issue involves cached authentication state not being invalidated during global session revocation, ensure that sessions are properly revoked by restarting the Mattermost service or forcing client reconnections to clear cached WebSocket sessions.

Compliance Impact

This vulnerability allows a user with an existing WebSocket connection to remain authenticated and continue receiving real-time events even after a global session revocation. This failure to invalidate cached authentication state could potentially lead to unauthorized access to sensitive information.

Such unauthorized access risks may impact compliance with standards and regulations like GDPR and HIPAA, which require strict control over user sessions and protection of personal and sensitive data. However, specific impacts on compliance are not detailed in the provided information.

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