CVE-2026-6673

What it is

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

At a glance

Exploitability

Can be exploited over the network with a low-privilege account, but needs a user to act. High risk of data tampering, service disruption.

Exploit odds

0.3% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-06-22 14:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-23 20:49 UTC Last updatedMost recent change to the record

Details

Published

2026-06-22 14:17 UTC

Last modified

2026-06-23 20:49 UTC

Exploit probability

0.3% · EPSS, next 30 days

Weakness

CWE-306 · Missing authentication

Record status

Analyzed

Affected

• Mattermost Server < 10.11.18
• Mattermost Server < 11.5.6
• Mattermost Server < 11.6.3
• Mattermost Server < 11.7.1

Attack profile CVSS 3.1 · 6.4

Attack vector

Network

Complexity

High

Privileges needed

Low

User interaction

Required

Scope

Unchanged

Confidentiality

None

Integrity

High

Availability

High