What is CVE-2026-9820?

CVE-2026-9820 is a low-severity vulnerability in Mattermost, classified under Missing Authorization. CVSS score: 3.8/10. Published 2026-07-13.

How severe is CVE-2026-9820?

Low severity. CVSS v3 base score is 3.8 out of 10.

Auth bypass in Mattermost

CVE-2026-9820

Mattermost versions 11.7.x <= 11.7.2, 10.11.x <= 10.11.19 fail to sanitize team objects returned by the scheme teams endpoint, which allows a user with the User Manager role to obtain invite links for private teams and use them to join or share access to those teams via the scheme teams API endpoint.. Mattermost Advisory ID: MMSA-2026-00671

Vulnerability class: Broken Access Control

EPSS: 0.003 (16.8th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 3.8 (Low). Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:N.

Affected products

Mattermost — versions 11.7.0, 10.11.0, 11.8.0
Mattermost Mattermost_server

Weakness classification (CWE)

CWE-862 — Missing Authorization

References

responsibledisclosure@mattermost.com (vendor-advisory, Vendor Advisory)

Frequently asked questions

What is CVE-2026-9820?: CVE-2026-9820 is a low-severity vulnerability in Mattermost, classified under Missing Authorization. CVSS score: 3.8/10. Published 2026-07-13.
How severe is CVE-2026-9820?: Low severity. CVSS v3 base score is 3.8 out of 10.