What’s Vulnerable › Vulnerabilities
CVE-2026-18223: Mattermost invitation tokens not bound to invited email address allowing unauthorized team and private channel access
- Severity: medium (CVSS 5.0 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.2% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-10-16 · updated 2026-10-29
- Weakness: CWE-863
Description
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to validate the invited recipient's email address when redeeming team and guest invitation tokens, which allows an authenticated attacker to join a team or gain unauthorized access to private channels via a forwarded or leaked invitation link.. Mattermost Advisory ID: MMSA-2026-00747
Affected products
- Mattermost: from 11.7.0 before 11.7.10; from 11.8.0 before 11.8.6; from 11.9.0 before 11.9.2; 11.10.0 (and their updates) — fixed in 11.7.10, 11.8.6, 11.9.2
- Mattermost: from 11.10.0 through 11.10.0; from 11.7.0 through 11.7.9; from 11.9.0 through 11.9.1; from 11.8.0 through 11.8.5
How to fix
Upgrade to a fixed version: Mattermost 11.7.10, 11.8.6, 11.9.2. Check the vendor advisory for mitigations.
References
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