Medium severity · published Oct 16, 2026
CVE-2026-18223
Mattermost invitation tokens not bound to invited email address allowing unauthorized team and private channel access
5.0
CVSS
0.2%
EPSS
No
On KEV
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
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:L/A:N
Attack vector
Network
Complexity
High
Privileges
High
User interaction
None
Confidentiality
High
Integrity
Low
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 5% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
Mattermost · Mattermost
11.10.0 through 11.10.0; 11.7.0 through 11.7.9; 11.9.0 through 11.9.1; 11.8.0 through 11.8.5 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-18223
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-18223
mattermost.com
https://mattermost.com/security-updates
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