CVE-2026-6673 PUBLISHED

Mattermost Jira plugin had unauthenticated {{/ac/installed}} lifecycle callback during pending Jira Cloud install

Assigner: Mattermost
Reserved: 20.04.2026 Published: 22.06.2026 Updated: 22.06.2026

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

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:H/A:H
CVSS Score: 6.4

Attack Vector	Network	Scope	Unchanged
Attack Complexity	High	Confidentiality Impact	None
Privileges Required	Low	Integrity Impact	High
User Interaction	Required	Availability Impact	High

CVSS 3.1

Product Status

Vendor	Mattermost
Product	Mattermost
Versions	Default: unaffected affected from 11.7.0 to 11.7.0 (incl.) affected from 11.6.0 to 11.6.2 (incl.) affected from 11.5.0 to 11.5.5 (incl.) affected from 10.11.0 to 10.11.17 (incl.) Version 11.8.0 is unaffected Version 11.7.1 is unaffected Version 11.6.3 is unaffected Version 11.5.6 is unaffected Version 10.11.18 is unaffected

Solutions

Update Mattermost to versions 11.8.0, 11.7.1, 11.6.3, 11.5.6, 10.11.18 or higher.

Credits

insomnia1102 finder

References

MMSA-2026-00654

Problem Types

CWE-306: Missing Authentication for Critical Function CWE