CVE-2026-2457: Github.com/mattermost/mattermost/server/v8 Mattermost Allows Attackers To Spoof Vulnerability
MODERATECVE-2026-2457 is a MODERATE (CVSS 4.3) mattermost allows attackers to spoof vulnerability (CWE-346: Origin Validation Error) affecting Github.com/mattermost/mattermost/server/v8 libraries in the Go ecosystem. The issue involves mattermost allows attackers to spoof permalink embeds. Remediation is available by upgrading affected packages to version 8.0.0-20260123211116-9efe617be8b8, 5.3.2-0.20260123211116-9efe617be8b8, 10.11.11, 11.2.3, 11.3.1.
CVE-2026-2457 at a Glance
Security Impact
CVSS: 4.3
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N).
How to Fix CVE-2026-2457
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 8.0.0-20260123211116-9efe617be8b8Upgrade github.com/mattermost/mattermost-server to 5.3.2-0.20260123211116-9efe617be8b8Upgrade github.com/mattermost/mattermost-server to 10.11.11Upgrade github.com/mattermost/mattermost-server to 11.2.3Upgrade github.com/mattermost/mattermost-server to 11.3.1Run 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-2026-2457, 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 8.0.0-20260123211116-9efe617be8b8), 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-346: Origin Validation Error, where the product does not properly verify that the source of data or communication is valid. 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-2026-2457 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 |
< 8.0.0-20260123211116-9efe617be8b8
|
8.0.0-20260123211116-9efe617be8b8
|
|
github.com/mattermost/mattermost-server
|
Go |
< 5.3.2-0.20260123211116-9efe617be8b8
|
5.3.2-0.20260123211116-9efe617be8b8
|
|
github.com/mattermost/mattermost-server
|
Go |
≥ 10.11.0-rc1
< 10.11.11
|
10.11.11
|
|
github.com/mattermost/mattermost-server
|
Go |
≥ 11.2.0-rc1
< 11.2.3
|
11.2.3
|
|
github.com/mattermost/mattermost-server
|
Go |
≥ 11.3.0-rc1
< 11.3.1
|
11.3.1
|
References
Frequently Asked Questions
What is CVE-2026-2457?
Which Github.com/mattermost/mattermost/server/v8 versions are affected?
What version fixes CVE-2026-2457?
Is github.com/mattermost/mattermost/server/v8 affected?
Is github.com/mattermost/mattermost-server affected?
What is the CVSS score of CVE-2026-2457?
What CWE is associated with CVE-2026-2457?
How can I check Go dependencies for CVE-2026-2457?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-ph22-fw5m-w2q9",
"modified" : "2026-03-17T20:00:12Z",
"published" : "2026-03-16T15:30:42Z",
"aliases" : [ "CVE-2026-2457" ],
"summary" : "Mattermost allows attackers to spoof permalink embeds",
"details" : "Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to sanitize client-supplied post metadata which allows an authenticated attacker to spoof permalink embeds impersonating other users via crafted PUT requests to the post update API endpoint. Mattermost Advisory ID: MMSA-2025-00569",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:L/PR:L/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" : "0"
}, {
"fixed" : "8.0.0-20260123211116-9efe617be8b8"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "5.3.2-0.20260123211116-9efe617be8b8"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "10.11.0-rc1"
}, {
"fixed" : "10.11.11"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "11.2.0-rc1"
}, {
"fixed" : "11.2.3"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "11.3.0-rc1"
}, {
"fixed" : "11.3.1"
} ]
} ]
} ],
"references" : [ {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-2457"
}, {
"type" : "WEB",
"url" : "https://github.com/mattermost/mattermost/commit/9efe617be8b8f1d036e12721e8e73b69a543ed34"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/mattermost/mattermost"
}, {
"type" : "WEB",
"url" : "https://mattermost.com/security-updates"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-346" ],
"severity" : "MODERATE",
"github_reviewed" : true,
"github_reviewed_at" : "2026-03-17T20:00:12Z",
"nvd_published_at" : "2026-03-16T14:19:29Z"
}
}