What is CVE-2026-3590?

CVE-2026-3590 is a medium-severity vulnerability in Mattermost, classified under Time-of-check Time-of-use (TOCTOU) Race Condition. CVSS score: 6.5/10. Published 2026-04-15.

How severe is CVE-2026-3590?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Vulnerability in Mattermost

CVE-2026-3590

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

Vulnerability class: TOCTOU (Time-of-Check to Time-of-Use)

EPSS: 0.001 (4.2th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.

Affected products

Mattermost — versions 10.11.0, 11.5.0, 11.4.0
Mattermost Mattermost_server

Weakness classification (CWE)

CWE-367 — Time-of-check Time-of-use (TOCTOU) Race Condition

References

responsibledisclosure@mattermost.com (vendor-advisory, Vendor Advisory)

Frequently asked questions

What is CVE-2026-3590?: CVE-2026-3590 is a medium-severity vulnerability in Mattermost, classified under Time-of-check Time-of-use (TOCTOU) Race Condition. CVSS score: 6.5/10. Published 2026-04-15.
How severe is CVE-2026-3590?: Medium severity. CVSS v3 base score is 6.5 out of 10.