CVE-2026-18223

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

State: Published
Severity: 5.0 Medium
Published: Oct 16, 2026
Updated: Oct 16, 2026
Reserved: Jul 29, 2026

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

Scores

CVSS	Score	Vector	Source
3.1	5.0 Medium	CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:L/A:N	Mattermost

Weaknesses

CWE-863 Incorrect Authorization

Affected Products

Product	Versions
MattermostMattermost	11.10.0 through 11.10.0Affected 11.7.0 through 11.7.9Affected 11.9.0 through 11.9.1Affected 11.8.0 through 11.8.5Affected 11.11.0Not affected 11.10.1Not affected 11.7.10Not affected 11.9.2Not affected 11.8.6Not affected

References

MMSA-2026-00747vendor-advisory

Every record here comes from the CVE Program’s CVE List. © 1999–2026 The MITRE Corporation. CVE is a registered trademark of The MITRE Corporation. The records are reproduced under the CVE Program terms of use.