CVE-2026-4273: Github.com/mattermost/mattermost/server/v8 Mattermost Doesn't Validate That The Vulnerability
LOWCVE-2026-4273 is a LOW (CVSS 3.7) mattermost doesn't validate that the vulnerability (CWE-863: Incorrect Authorization) affecting Github.com/mattermost/mattermost/server/v8 libraries in the Go ecosystem. The issue involves mattermost doesn't validate that the refreshedtoken differs from the original invite token during remote cluster invite confirmation. Remediation is available by upgrading affected packages to version 11.5.2, 5.3.2-0.20260313190740-742e0be95074, 10.11.14, 8.0.0-20260313190740-742e0be95074.
CVE-2026-4273 at a Glance
Security Impact
CVSS: 3.7
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N).
How to Fix CVE-2026-4273
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 to 5.3.2-0.20260313190740-742e0be95074Upgrade github.com/mattermost/mattermost/server/v8 to 10.11.14Upgrade github.com/mattermost/mattermost/server/v8 to 8.0.0-20260313190740-742e0be95074Run 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-2026-4273, 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-863: Incorrect Authorization, where the product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. 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-2026-4273 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
|
Go |
< 5.3.2-0.20260313190740-742e0be95074
|
5.3.2-0.20260313190740-742e0be95074
|
|
github.com/mattermost/mattermost/server/v8
|
Go |
≥ 10.11.0
< 10.11.14
|
10.11.14
|
|
github.com/mattermost/mattermost/server/v8
|
Go |
< 8.0.0-20260313190740-742e0be95074
|
8.0.0-20260313190740-742e0be95074
|
References
Frequently Asked Questions
What is CVE-2026-4273?
Which Github.com/mattermost/mattermost/server/v8 versions are affected?
What version fixes CVE-2026-4273?
Is github.com/mattermost/mattermost/server/v8 affected?
Is github.com/mattermost/mattermost-server affected?
What is the CVSS score of CVE-2026-4273?
What CWE is associated with CVE-2026-4273?
How can I check Go dependencies for CVE-2026-4273?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-hqpj-f3jh-29vx",
"modified" : "2026-06-01T15:53:25Z",
"published" : "2026-05-18T09:31:47Z",
"aliases" : [ "CVE-2026-4273" ],
"summary" : "Mattermost doesn't validate that the RefreshedToken differs from the original invite token during remote cluster invite confirmation",
"details" : "Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to validate that the RefreshedToken differs from the original invite token during remote cluster invite confirmation which allows an authenticated attacker to bypass token rotation and reuse the original invite token via sending a crafted invite confirmation with a RefreshedToken matching the original token. Mattermost Advisory ID: MMSA-2026-00575",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/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" : "8.0.0-20260313190740-742e0be95074"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "5.3.2-0.20260313190740-742e0be95074"
} ]
} ]
} ],
"references" : [ {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-4273"
}, {
"type" : "WEB",
"url" : "https://github.com/mattermost/mattermost/commit/742e0be9507454a7e662668e1d9ec1b94b636e9b"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/mattermost/mattermost"
}, {
"type" : "WEB",
"url" : "https://mattermost.com/security-updates"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-863" ],
"severity" : "LOW",
"github_reviewed" : true,
"github_reviewed_at" : "2026-06-01T15:53:25Z",
"nvd_published_at" : "2026-05-18T08:16:14Z"
}
}