CVE-2026-6673
Received Received - Intake
Authentication Bypass in Mattermost via Atlassian Connect Callback

Publication date: 2026-06-22

Last updated on: 2026-06-22

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
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Meta Information
Published
2026-06-22
Last Modified
2026-06-22
Generated
2026-06-22
AI Q&A
2026-06-22
EPSS Evaluated
N/A
NVD
CVE-2026-6673
EUVD
EUVD-2026-38249
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
mattermost mattermost to 10.11.17 (inc)
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Exploitability
CWE
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KEV
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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.
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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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