CVE-2026-6673

Name: CVE-2026-6673
Creator: NVD / NIST
Published: 2026-06-22T14:17:51.26+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.4/10EPSS 0.18%

Last modified Jun 23, 2026

CVE-2026-6673 is a medium-severity vulnerability rated 6.4/10 on the CVSS scale. 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. EPSS estimates a 0.18% chance of exploitation in the next 30 days.

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

Metrics

CVSS 3.1

6.4/10

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

EPSS Probability

0.18%

7.5th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-306

Affected Software

Vendor	Product	Versions
Mattermost	Mattermost Server	>= 10.11.0, < 10.11.18
Mattermost	Mattermost Server	>= 11.5.0, < 11.5.6
Mattermost	Mattermost Server	>= 11.6.0, < 11.6.3
Mattermost	Mattermost Server	>= 11.7.0, < 11.7.1

References

https://mattermost.com/security-updatesVendor Advisory

Timeline

Published: Jun 22, 2026
Last Modified: Jun 23, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-6673?

How severe is CVE-2026-6673?

CVE-2026-6673 has a CVSS score of 6.4/10 (MEDIUM severity). The EPSS model estimates a 0.18% probability of exploitation in the next 30 days.

How do I fix CVE-2026-6673?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-6673?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST