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

Published 2026-07-13 · last modified 2026-07-13.

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.

EPSS exploit prediction

EPSS: 0.003 (15.7th percentile), scored 2026-10-12.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 16th percentile — 15.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: 0.000

Affected products

Mattermost — versions 11.7.0, 10.11.0, 11.8.0
Mattermost Server

Weakness classification (CWE)

CWE-862 — Missing Authorization

References

mattermost.com/security-updates (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.