CVE-2026-6673

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

Score

CVSS 3.1 6.4 Medium

Status

Analyzed - responsibledisclosure@mattermost.com

Published

2026-06-22

Last modified

2026-06-22

Weaknesses

CWE-306

Affected products

• Mattermost (Mattermost)
• Mattermost Server (Mattermost)

References

• https://mattermost.com/security-updates