CVE-2026-9820: Mattermost schemes teams endpoint exposes private team invite IDs

Severity: low (CVSS 3.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-13 · updated 2026-07-13
Weakness: CWE-862

Description

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

Affected products

Mattermost: from 10.11.0 before 10.11.20; from 11.7.0 before 11.7.3 — fixed in 10.11.20, 11.7.3

How to fix

Upgrade to a fixed version: Mattermost 10.11.20, 11.7.3. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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