Is CVE-2026-21388 actively exploited?

CVE-2026-21388 has no public evidence of in-the-wild exploitation as of 2026-04-25.

What is the CVSS score for CVE-2026-21388?

CVE-2026-21388 has a CVSS score of 3.7 (LOW severity). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L.

How do I patch CVE-2026-21388?

Patch guidance is available from mattermost security advisories. CVEDatabase generates AI-assisted remediation guidance on demand for CVE-2026-21388.

Which products are affected by CVE-2026-21388?

1 product: mattermost mattermost server.

CVE-2026-21388 - remediation guidance & executive summary

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

CVSS Metrics

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
Attack Vector: network
Complexity: high
Privileges: none
User Action: none
Scope: unchanged
Confidentiality: none
Integrity: none
Availability: low
Weaknesses: CWE-770

Metadata

Primary Vendor: MATTERMOST
Published: 4/9/2026
Last Modified: 4/25/2026
Source: NIST NVD
Note: Verify all details with official vendor sources before applying patches.

Affected Products

mattermost : mattermost_server

Remediation Guidance

Executive Summary

Cite this page

CVE-2026-21388. CVEDatabase.com. Retrieved 1 May 2026. https://cvedatabase.com/cve/CVE-2026-21388

View on NIST NVD

CVE-2026-21388 vulnerability