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…

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

EPSS: 0.000 (11.5th 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

Weakness classification (CWE)

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

References

MMSA-2026-00624 (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.