CVE-2026-6673

Analyzed Analyzed - Analysis Complete

Authentication Bypass in Mattermost via Atlassian Connect Callback

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 authenticate Atlassian Connect installed callbacks, allowing a remote unauthenticated attacker to inject a rogue sharedSecret and disrupt the Jira integration via POST to /ac/installed during the pending-install window.. Mattermost Advisory ID: MMSA-2026-00654

CVSS Scores

EPSS Scores

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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-2026-6673

EUVD

EUVD-2026-38249

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-306	The product does not perform any authentication for functionality that requires a provable user identity or consumes a significant amount of resources.

Attack-Flow Graph

Executive Summary

This vulnerability affects certain versions of Mattermost (11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17) where the system fails to properly authenticate Atlassian Connect installed callbacks.

Because of this failure, a remote unauthenticated attacker can inject a rogue sharedSecret by sending a POST request to the /ac/installed endpoint during the pending-install window.

This allows the attacker to disrupt the Jira integration with Mattermost.

Impact Analysis

An attacker exploiting this vulnerability can disrupt the Jira integration in Mattermost by injecting a rogue sharedSecret.

This disruption could lead to denial of service or interference with normal communication between Mattermost and Jira.

The CVSS score indicates a moderate severity with high impact on integrity and availability, meaning the attacker can cause significant disruption but cannot directly compromise confidentiality.

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