CVE-2026-3590: Github.com/mattermost/mattermost/server/v8 Remote Code Execution Vulnerability
MODERATECVE-2026-3590 is a MODERATE (CVSS 6.5) remote code execution vulnerability (CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition) affecting Github.com/mattermost/mattermost/server/v8 libraries in the Go ecosystem. The issue involves mattermost has session spoofing due to lack of single-use consumption of guest magic link tokens enforcement. Remediation is available by upgrading affected packages to version 8.0.0-20250723052842-4cb8d8940332, 10.11.13, 11.5.0, 11.4.3, 11.3.3.
CVE-2026-3590 at a Glance
Security Impact
CVSS: 6.5
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:L/I:L/A:N).
How to Fix CVE-2026-3590
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 8.0.0-20250723052842-4cb8d8940332Upgrade github.com/mattermost/mattermost-server to 10.11.13Upgrade github.com/mattermost/mattermost-server to 11.5.0Upgrade github.com/mattermost/mattermost-server to 11.4.3Upgrade github.com/mattermost/mattermost-server to 11.3.3Run 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-2026-3590, 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 8.0.0-20250723052842-4cb8d8940332), 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-367: Time-of-check Time-of-use (TOCTOU) Race Condition, where the product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of 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-2026-3590 Affected Github.com/mattermost/mattermost/server/v8 Versions
5 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
github.com/mattermost/mattermost/server/v8
|
Go |
≥ 8.0.0-20250721062209-4952acea88ce
< 8.0.0-20250723052842-4cb8d8940332
|
8.0.0-20250723052842-4cb8d8940332
|
|
github.com/mattermost/mattermost-server
|
Go |
≥ 10.11.0-rc1
< 10.11.13
|
10.11.13
|
|
github.com/mattermost/mattermost-server
|
Go |
≥ 11.5.0-rc1
< 11.5.0
All 1 versions
11.5.0-rc1
|
11.5.0
|
|
github.com/mattermost/mattermost-server
|
Go |
≥ 11.4.0-rc1
< 11.4.3
|
11.4.3
|
|
github.com/mattermost/mattermost-server
|
Go |
≥ 11.3.0-rc1
< 11.3.3
|
11.3.3
|
References
Frequently Asked Questions
What is CVE-2026-3590?
Which Github.com/mattermost/mattermost/server/v8 versions are affected?
What version fixes CVE-2026-3590?
Is github.com/mattermost/mattermost/server/v8 affected?
Is github.com/mattermost/mattermost-server affected?
What is the CVSS score of CVE-2026-3590?
What CWE is associated with CVE-2026-3590?
How can I check Go dependencies for CVE-2026-3590?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-mh4x-rmrx-3hp4",
"modified" : "2026-04-28T22:57:43Z",
"published" : "2026-04-17T15:31:17Z",
"aliases" : [ "CVE-2026-3590" ],
"summary" : "Mattermost has session spoofing due to lack of single-use consumption of guest magic link tokens enforcement",
"details" : "Mattermost versions 10.11.x <= 10.11.12, 11.5.x <= 11.5.0, 11.4.x <= 11.4.2, 11.3.x <= 11.3.2 fail to enforce atomic single-use consumption of guest magic link tokens, which allows an attacker with access to a valid magic link to establish multiple independent authenticated sessions via concurrent requests. Mattermost Advisory ID: MMSA-2026-00624.",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost/server/v8"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "8.0.0-20250721062209-4952acea88ce"
}, {
"fixed" : "8.0.0-20250723052842-4cb8d8940332"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "10.11.0-rc1"
}, {
"fixed" : "10.11.13"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "11.5.0-rc1"
}, {
"fixed" : "11.5.0"
} ]
} ],
"versions" : [ "11.5.0-rc1" ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "11.4.0-rc1"
}, {
"fixed" : "11.4.3"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "11.3.0-rc1"
}, {
"fixed" : "11.3.3"
} ]
} ]
} ],
"references" : [ {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-3590"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/mattermost/mattermost"
}, {
"type" : "WEB",
"url" : "https://mattermost.com/security-updates"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-367" ],
"severity" : "MODERATE",
"github_reviewed" : true,
"github_reviewed_at" : "2026-04-28T22:57:43Z",
"nvd_published_at" : "2026-04-15T12:16:40Z"
}
}