CVE-2026-6673 | Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5… | CVSS 6.4 MEDIUM

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

Metadata

CVE ID: CVE-2026-6673
State: PUBLISHED
Assigner: Mattermost
Reserved: 2026-04-20 13:45 UTC
Published: 2026-06-22 13:38 UTC
Last updated: 2026-06-22 15:41 UTC
Primary CWE: CWE-306
CWE-306: Missing Authentication for Critical Function
Vendor / Product: Mattermost / Mattermost
Sources: cve.org · NVD

Severity & Metrics

6.4 MEDIUM CVSS 3.1

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

SSVC — CISA Coordinator

Exploitation: none
Automatable: no
Tech. Impact: partial

Affected products (1)

Vendor	Product	Platform	Versions
Mattermost	Mattermost	—	11.7.0 ≤ 11.7.0, 11.6.0 ≤ 11.6.2, 11.5.0 ≤ 11.5.5, 10.11.0 ≤ 10.11.17 …

Weakness (CWE)

CWE	Source	Description
CWE-306	cna	CWE-306: Missing Authentication for Critical Function

CVSS scores (1)

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

References (1)

MMSA-2026-00654 https://mattermost.com/security-updates