CVE-2026-4273: Insufficient token rotation validation in remote cluster invite confirmation

Severity: medium (CVSS 4.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-18 · updated 2026-10-14
Weakness: CWE-863

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

Affected products

Mattermost: from 10.11.0 before 10.11.14; from 11.5.0 before 11.5.2 — fixed in 10.11.14, 11.5.2

How to fix

Upgrade to a fixed version: Mattermost 10.11.14, 11.5.2. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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