CVE-2026-6334: Github.com/mattermost/mattermost/server/v8 Remote Code Execution Vulnerability
LOWCVE-2026-6334 is a LOW (CVSS 3.1) remote code execution vulnerability (CWE-305: Authentication Bypass by Primary Weakness) affecting Github.com/mattermost/mattermost/server/v8 libraries in the Go ecosystem. The issue involves mattermost doesn't enforce client identity binding during the oauth authorization code redemption flow. Remediation is available by upgrading affected packages to version 11.5.2, 10.11.14, 8.0.0-20260318173148-e9ae890a013b, 5.3.2-0.20260318173148-e9ae890a013b.
CVE-2026-6334 at a Glance
Security Impact
CVSS: 3.1
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:L/I:L/A:N).
How to Fix CVE-2026-6334
To remediate this vulnerability, upgrade all affected Github.com/mattermost/mattermost/server/v8 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/v8 to 11.5.2Upgrade github.com/mattermost/mattermost/server/v8 to 10.11.14Upgrade github.com/mattermost/mattermost/server/v8 to 8.0.0-20260318173148-e9ae890a013bUpgrade github.com/mattermost/mattermost-server to 5.3.2-0.20260318173148-e9ae890a013bRun the following command in your project directory to verify that all resolved dependencies use the patched release:
inspect dependencies for github.com/mattermost/mattermost/server/v8How to Check if You Are Affected
To determine whether your application is affected by CVE-2026-6334, inspect your project dependencies for Github.com/mattermost/mattermost/server/v8:
inspect dependencies for github.com/mattermost/mattermost/server/v8Analyze the terminal output to locate any version of Github.com/mattermost/mattermost/server/v8 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 11.5.2), 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-305: Authentication Bypass by Primary Weakness, where the authentication algorithm is sound, but the implemented mechanism can be bypassed as the result of a separate weakness that is primary to the authentication error. In Github.com/mattermost/mattermost/server/v8, 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-2026-6334 Affected Github.com/mattermost/mattermost/server/v8 Versions
4 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
github.com/mattermost/mattermost/server/v8
|
Go |
≥ 11.5.0
< 11.5.2
|
11.5.2
|
|
github.com/mattermost/mattermost/server/v8
|
Go |
≥ 10.11.0
< 10.11.14
|
10.11.14
|
|
github.com/mattermost/mattermost/server/v8
|
Go |
< 8.0.0-20260318173148-e9ae890a013b
|
8.0.0-20260318173148-e9ae890a013b
|
|
github.com/mattermost/mattermost-server
|
Go |
< 5.3.2-0.20260318173148-e9ae890a013b
|
5.3.2-0.20260318173148-e9ae890a013b
|
References
Frequently Asked Questions
What is CVE-2026-6334?
Which Github.com/mattermost/mattermost/server/v8 versions are affected?
What version fixes CVE-2026-6334?
Is github.com/mattermost/mattermost/server/v8 affected?
Is github.com/mattermost/mattermost-server affected?
What is the CVSS score of CVE-2026-6334?
What CWE is associated with CVE-2026-6334?
How can I check Go dependencies for CVE-2026-6334?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-jp3f-x449-4q75",
"modified" : "2026-06-01T15:04:49Z",
"published" : "2026-05-18T09:31:47Z",
"aliases" : [ "CVE-2026-6334" ],
"summary" : "Mattermost doesn't enforce client identity binding during the OAuth authorization code redemption flow",
"details" : "Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to enforce client identity binding during the OAuth authorization code redemption flow which allows an authenticated OAuth client to redeem authorization codes issued to a different client via a crafted token exchange request.. Mattermost Advisory ID: MMSA-2026-00570",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:L/I:L/A:N"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost/server/v8"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "11.5.0"
}, {
"fixed" : "11.5.2"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost/server/v8"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "10.11.0"
}, {
"fixed" : "10.11.14"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost/server/v8"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "8.0.0-20260318173148-e9ae890a013b"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "5.3.2-0.20260318173148-e9ae890a013b"
} ]
} ]
} ],
"references" : [ {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-6334"
}, {
"type" : "WEB",
"url" : "https://github.com/mattermost/mattermost/commit/e9ae890a013bb57989fcbdb548d8b7b86b240237"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/mattermost/mattermost"
}, {
"type" : "WEB",
"url" : "https://mattermost.com/security-updates"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-305" ],
"severity" : "LOW",
"github_reviewed" : true,
"github_reviewed_at" : "2026-06-01T15:04:48Z",
"nvd_published_at" : "2026-05-18T08:16:14Z"
}
}