CVE-2026-5308

HIGH

Mattermost doesn't enforce request body size limits on plugin HTTP endpoints

Published May 26, 2026Updated July 7, 2026Source: osv

Summary

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to enforce request body size limits on plugin HTTP endpoints which allows an attacker to cause a denial of service via crafted oversized HTTP requests.. Mattermost Advisory ID: MMSA-2026-00646

Remediation

Upgrade to the fixed version using your package manager.

Update github.com/mattermost/mattermost-server to 10.11.15 or later

go get github.com/mattermost/mattermost-server@v10.11.15

Update github.com/mattermost/mattermost-plugin-github to 1.0.1-0.20260410143745-9b41b1fd43c4 or later

go get github.com/mattermost/mattermost-plugin-github@v1.0.1-0.20260410143745-9b41b1fd43c4

Update github.com/mattermost/mattermost-server to 11.6.1 or later

go get github.com/mattermost/mattermost-server@v11.6.1

Update github.com/mattermost/mattermost-server to 11.5.4 or later

go get github.com/mattermost/mattermost-server@v11.5.4

Update github.com/mattermost/mattermost-server to 11.4.5 or later

go get github.com/mattermost/mattermost-server@v11.4.5

After upgrading, run your dependency scanner again to confirm the vulnerability is resolved.

Affected Packages (5)

Package	Ecosystem	Affected	Fixed In
github.com/mattermost/mattermost-server	go	All versions	10.11.15
github.com/mattermost/mattermost-plugin-github	go	All versions	1.0.1-0.20260410143745-9b41b1fd43c4
github.com/mattermost/mattermost-server	go	11.6.0	11.6.1
github.com/mattermost/mattermost-server	go	All versions	11.5.4
github.com/mattermost/mattermost-server	go	All versions	11.4.5

Vulnerability Classification

Common Weakness Enumeration (CWE) identifiers for this vulnerability type.

CWE-400
Uncontrolled Resource ConsumptionMITRE

CVSS Score Breakdown

What the CVSS (Common Vulnerability Scoring System) 7.5 score means for each attack dimension.

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

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

References

Frequently Asked Questions

What is CVE-2026-5308?: Mattermost doesn't enforce request body size limits on plugin HTTP endpoints This vulnerability has been assigned a severity rating of HIGH (CVSS score: 7.5/10).
How do I check if my project is affected by CVE-2026-5308?: CVE-2026-5308 affects github.com/mattermost/mattermost-server and github.com/mattermost/mattermost-plugin-github. Use GeekWala's free vulnerability scanner to check your dependencies against CVE-2026-5308 and 200,000+ other known vulnerabilities.

Severity & Exploitability

CVSS Score

7.5

High exploitability or significant impact. Prioritize remediation within days.

Also Known As

GHSA-jmvr-r5hm-fxfr

GO-2026-5836

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