CVE-2026-18223

medium

Assigned by CNA: mattermost

Published 2026-10-16 · Modified 2026-10-16

Discuss on Community Propose mitigation

CVSS v3

5.0

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

CVSS v4 NEW

—

not yet in upstream

VIR risk

5.0

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

Predictions

Exploit likelihood

60%

Patch ETA

—

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

No mitigations published for this CVE yet.

The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.

Propose a mitigation on Community Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here with source_tier=community-verified.

References

https://mattermost.com/security-updates

CWEs

CWE-863

Community-verified mitigations for this CVE will appear above when contributors publish them.

Verify integrity in audit chain (admin only). AS-IS.