CVE-2026-5308: Github.com/mattermost/mattermost server Remote Code Execution Vulnerability
HIGHCVE-2026-5308 is a HIGH (CVSS 7.5) remote code execution vulnerability (CWE-400: Uncontrolled Resource Consumption) affecting Github.com/mattermost/mattermost server libraries in the Go ecosystem. The issue involves mattermost doesn't enforce request body size limits on plugin http endpoints. Remediation is available by upgrading affected packages to version 11.6.1, 11.5.4, 11.4.5, 10.11.15, 1.0.1-0.20260410143745-9b41b1fd43c4.
CVE-2026-5308 at a Glance
Security Impact
CVSS: 7.5
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
How to Fix CVE-2026-5308
To remediate this vulnerability, upgrade all affected Github.com/mattermost/mattermost server dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
Upgrade github.com/mattermost/mattermost-server to 11.6.1Upgrade github.com/mattermost/mattermost-server to 11.5.4Upgrade github.com/mattermost/mattermost-server to 11.4.5Upgrade github.com/mattermost/mattermost-server to 10.11.15Upgrade github.com/mattermost/mattermost-plugin-github to 1.0.1-0.20260410143745-9b41b1fd43c4Run the following command in your project directory to verify that all resolved dependencies use the patched release:
inspect dependencies for github.com/mattermost/mattermost-serverHow to Check if You Are Affected
To determine whether your application is affected by CVE-2026-5308, inspect your project dependencies for Github.com/mattermost/mattermost server:
inspect dependencies for github.com/mattermost/mattermost-serverAnalyze the terminal output to locate any version of Github.com/mattermost/mattermost server in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 11.6.1), your application is affected.
Note: Verify declared build manifests and deployed runtime container environments.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-400: Uncontrolled Resource Consumption, where the product does not properly control the allocation and maintenance of a limited resource. In Github.com/mattermost/mattermost server, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
CVE-2026-5308 Affected Github.com/mattermost/mattermost server Versions
5 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
github.com/mattermost/mattermost-server
|
Go |
≥ 11.6.0
< 11.6.1
All 1 versions
11.6.0
|
11.6.1
|
|
github.com/mattermost/mattermost-server
|
Go |
≥ 11.5.0
< 11.5.4
|
11.5.4
|
|
github.com/mattermost/mattermost-server
|
Go |
≥ 11.4.0
< 11.4.5
|
11.4.5
|
|
github.com/mattermost/mattermost-server
|
Go |
≥ 10.11.0
< 10.11.15
|
10.11.15
|
|
github.com/mattermost/mattermost-plugin-github
|
Go |
< 1.0.1-0.20260410143745-9b41b1fd43c4
|
1.0.1-0.20260410143745-9b41b1fd43c4
|
References
Frequently Asked Questions
What is CVE-2026-5308?
Which Github.com/mattermost/mattermost server versions are affected?
What version fixes CVE-2026-5308?
Is github.com/mattermost/mattermost-server affected?
Is github.com/mattermost/mattermost-plugin-github affected?
What is the CVSS score of CVE-2026-5308?
What CWE is associated with CVE-2026-5308?
How can I check Go dependencies for CVE-2026-5308?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-jmvr-r5hm-fxfr",
"modified" : "2026-06-29T22:41:48Z",
"published" : "2026-05-26T13:30:15Z",
"aliases" : [ "CVE-2026-5308" ],
"summary" : "Mattermost doesn't enforce request body size limits on plugin HTTP endpoints",
"details" : "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",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "11.6.0"
}, {
"fixed" : "11.6.1"
} ]
} ],
"versions" : [ "11.6.0" ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "11.5.0"
}, {
"fixed" : "11.5.4"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "11.4.0"
}, {
"fixed" : "11.4.5"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "10.11.0"
}, {
"fixed" : "10.11.15"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-plugin-github"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "1.0.1-0.20260410143745-9b41b1fd43c4"
} ]
} ]
} ],
"references" : [ {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-5308"
}, {
"type" : "WEB",
"url" : "https://github.com/mattermost/mattermost-plugin-github/commit/9b41b1fd43c408f4be53026ee337bbeaa74ad47c"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/mattermost/mattermost"
}, {
"type" : "WEB",
"url" : "https://mattermost.com/security-updates"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-400" ],
"severity" : "HIGH",
"github_reviewed" : true,
"github_reviewed_at" : "2026-06-29T22:41:48Z",
"nvd_published_at" : "2026-05-22T11:16:23Z"
}
}