CVE-2026-3590: Race Condition in Guest Magic Link Authentication Allows Token Reuse

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-15 · updated 2026-06-17
Weakness: CWE-367

Description

Mattermost versions 10.11.x <= 10.11.12, 11.5.x <= 11.5.0, 11.4.x <= 11.4.2, 11.3.x <= 11.3.2 fail to enforce atomic single-use consumption of guest magic link tokens, which allows an attacker with access to a valid magic link to establish multiple independent authenticated sessions via concurrent requests.. Mattermost Advisory ID: MMSA-2026-00624

Affected products

Mattermost: from 10.11.0 before 10.11.13; from 11.3.0 before 11.3.3; from 11.4.0 before 11.4.3; from 11.5.0 before 11.5.1 — fixed in 10.11.13, 11.3.3, 11.4.3, 11.5.1

How to fix

Upgrade to a fixed version: Mattermost 10.11.13, 11.3.3, 11.4.3, 11.5.1. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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