CVE-2026-18223 PUBLISHED

Mattermost invitation tokens not bound to invited email address allowing unauthorized team and private channel access

Assigner: Mattermost
Reserved: 29.07.2026 Published: 16.10.2026 Updated: 16.10.2026

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

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:L/A:N
CVSS Score: 5

Attack Vector	Network	Scope	Unchanged
Attack Complexity	High	Confidentiality Impact	High
Privileges Required	High	Integrity Impact	Low
User Interaction	None	Availability Impact	None

CVSS 3.1

Product Status

Vendor	Mattermost
Product	Mattermost
Versions	Default: unaffected affected from 11.10.0 to 11.10.0 (incl.) affected from 11.7.0 to 11.7.9 (incl.) affected from 11.9.0 to 11.9.1 (incl.) affected from 11.8.0 to 11.8.5 (incl.) Version 11.11.0 is unaffected Version 11.10.1 is unaffected Version 11.7.10 is unaffected Version 11.9.2 is unaffected Version 11.8.6 is unaffected

Solutions

Update Mattermost to versions 11.11.0, 11.10.1, 11.7.10, 11.9.2, 11.8.6 or higher.

Credits

CERT PL finder

References

MMSA-2026-00747

Problem Types

CWE-863: Incorrect Authorization CWE