Medium severity · published May 18, 2026
CVE-2026-4273
Insufficient token rotation validation in remote cluster invite confirmation
4.3
CVSS
0.1%
EPSS
No
On KEV
Description
Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to validate that the RefreshedToken differs from the original invite token during remote cluster invite confirmation which allows an authenticated attacker to bypass token rotation and reuse the original invite token via sending a crafted invite confirmation with a RefreshedToken matching the original token. Mattermost Advisory ID: MMSA-2026-00575
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
None
Integrity
Low
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.1% · higher than 3% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
Mattermost · Mattermost
11.5.0 through 11.5.1; 10.11.0 through 10.11.13 · source: vendor
MS
Mattermost Server · Mattermost
10.11.0 before 10.11.14; 11.5.0 before 11.5.2 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-4273
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-4273
Vendor Advisory
https://mattermost.com/security-updates
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