What is CVE-2026-21388?

CVE-2026-21388 is a low-severity vulnerability in Mattermost, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 3.7/10. Published 2026-04-09.

How severe is CVE-2026-21388?

Low severity. CVSS v3 base score is 3.7 out of 10.

Resource exhaustion in Mattermost

CVE-2026-21388

Mattermost Plugins versions <=2.3.1 fail to limit the request body size on the {{/lifecycle}} webhook endpoint which allows an authenticated attacker to cause memory exhaustion and denial of service via sending an oversized JSON payload. M…

EPSS: 0.000 (4.9th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 3.7 (Low). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L.

Affected products

Mattermost — versions 0, 2.3.2.0

Weakness classification (CWE)

CWE-770 — Allocation of Resources Without Limits or Throttling

References

MMSA-2026-00610 (vendor-advisory)

Frequently asked questions

What is CVE-2026-21388?: CVE-2026-21388 is a low-severity vulnerability in Mattermost, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 3.7/10. Published 2026-04-09.
How severe is CVE-2026-21388?: Low severity. CVSS v3 base score is 3.7 out of 10.