CVE-2026-21388

Name: CVE-2026-21388
Creator: NVD / NIST
Published: 2026-04-09T11:16:20.897+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.5/10EPSS 0.31%

Last modified Jun 17, 2026

CVE-2026-21388 is a medium-severity vulnerability rated 6.5/10 on the CVSS scale. 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. Mattermost Advisory ID: MMSA-2026-00610. EPSS estimates a 0.31% chance of exploitation in the next 30 days.

Description

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. Mattermost Advisory ID: MMSA-2026-00610

Metrics

CVSS 3.1

6.5/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

0.31%

22.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-770

Affected Software

Vendor	Product	Versions
Mattermost	Mattermost Server	<= 2.3.1

References

https://mattermost.com/security-updatesVendor Advisory

Timeline

Published: Apr 9, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-21388?

How severe is CVE-2026-21388?

CVE-2026-21388 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 0.31% probability of exploitation in the next 30 days.

How do I fix CVE-2026-21388?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-21388?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST