Mattermost 11.7 Auth Bypass: Unauth POST /ac/installed SharedSecret
CVE-2026-6673 Published on June 22, 2026

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

Vendor Advisory NVD

Vulnerability Analysis

CVE-2026-6673 can be exploited with network access, requires user interaction and a small amount of user privileges. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality, a high impact on integrity and availability.

Attack Vector:
NETWORK
Attack Complexity:
HIGH
Privileges Required:
LOW
User Interaction:
REQUIRED
Scope:
UNCHANGED
Confidentiality Impact:
NONE
Integrity Impact:
HIGH
Availability Impact:
HIGH

Weakness Type

Missing Authentication for Critical Function

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


Products Associated with CVE-2026-6673

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MatterMost
 

Affected Versions

Mattermost: