CVE-2026-4055

Name: CVE-2026-4055
Creator: NVD / NIST
Published: 2026-05-21T08:16:23.13+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 4.3/10EPSS 0.15%

Last modified Jun 17, 2026

CVE-2026-4055 is a medium-severity vulnerability rated 4.3/10 on the CVSS scale. Mattermost versions 11.5.x <= 11.5.1 fail to validate team-level run_create permission against the target team when creating a playbook run which allows an authenticated team member to create runs in teams where they lack permission via specifying a different team ID in the run creation API request. Mattermost Advisory ID: MMSA-2026-00629. EPSS estimates a 0.15% chance of exploitation in the next 30 days.

Description

Mattermost versions 11.5.x <= 11.5.1 fail to validate team-level run_create permission against the target team when creating a playbook run which allows an authenticated team member to create runs in teams where they lack permission via specifying a different team ID in the run creation API request. Mattermost Advisory ID: MMSA-2026-00629

Metrics

CVSS 3.1

4.3/10

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

EPSS Probability

0.15%

4.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-863

Affected Software

Vendor	Product	Versions
Mattermost	Mattermost Server	>= 10.11.0, < 10.11.17
Mattermost	Mattermost Server	>= 11.5.0, < 11.5.5
Mattermost	Mattermost Server	>= 11.6.0, < 11.6.2

References

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

Timeline

Published: May 21, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-4055?

How severe is CVE-2026-4055?

CVE-2026-4055 has a CVSS score of 4.3/10 (MEDIUM severity). The EPSS model estimates a 0.15% probability of exploitation in the next 30 days.

How do I fix CVE-2026-4055?

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-2026-4055?

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

Scan your code now

Source: NVD / NIST