CVE-2025-12559: Github.com/mattermost/mattermost/server/v8 Mattermost Fails To Sanitize Team Vulnerability

MODERATE
Advisory Identifier: GHSA-4g87-9x45-cx2h
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CVSS 4.3
CWE-200
Published
Advisory Summary

CVE-2025-12559 is a MODERATE (CVSS 4.3) mattermost fails to sanitize team vulnerability (CWE-200: Exposure of Sensitive Information to an Unauthorized Actor) affecting Github.com/mattermost/mattermost/server/v8 libraries in the Go ecosystem. The issue involves mattermost fails to sanitize team email addresses. Remediation is available by upgrading affected packages to version 8.0.0-20251015091448-abbf01b9db45, 11.0.3, 10.12.2, 10.11.5, 10.5.13.

CVE-2025-12559 at a Glance

CVE Identifier CVE-2025-12559
GHSA Identifier GHSA-4g87-9x45-cx2h
Severity MODERATE
CVSS v3.1 Base Score 4.3
CWE Classification CWE-200: Exposure of Sensitive Information to an Unauthorized Actor
Affected Product Github.com/mattermost/mattermost/server/v8
Package Ecosystem Go
Published Date
Last Updated

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:L/I:N/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required Low (PR:L)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality Low (C:L)
Integrity None (I:N)
Availability None (A:N)

How to Fix CVE-2025-12559

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.

github.com/mattermost/mattermost/server/v8 fixed: 8.0.0-20251015091448-abbf01b9db45 
Upgrade github.com/mattermost/mattermost/server/v8 to 8.0.0-20251015091448-abbf01b9db45
github.com/mattermost/mattermost-server fixed: 11.0.3 
Upgrade github.com/mattermost/mattermost-server to 11.0.3
github.com/mattermost/mattermost-server fixed: 10.12.2 
Upgrade github.com/mattermost/mattermost-server to 10.12.2
github.com/mattermost/mattermost-server fixed: 10.11.5 
Upgrade github.com/mattermost/mattermost-server to 10.11.5
github.com/mattermost/mattermost-server fixed: 10.5.13 
Upgrade github.com/mattermost/mattermost-server to 10.5.13
Verify Direct and Transitive Dependencies

Run 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/v8

How to Check if You Are Affected

To determine whether your application is affected by CVE-2025-12559, inspect your project dependencies for Github.com/mattermost/mattermost/server/v8:

inspect dependencies for github.com/mattermost/mattermost/server/v8

Analyze 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 8.0.0-20251015091448-abbf01b9db45), 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-200: Exposure of Sensitive Information to an Unauthorized Actor, where the product exposes sensitive information to an actor that is not explicitly authorized to have access to that information. 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

Mattermost versions 11.0.x <= 11.0.2, 10.12.x <= 10.12.1, 10.11.x <= 10.11.4, 10.5.x <= 10.5.12 fail to sanitize team email addresses to be visible only to Team Admins, which allows any authenticated user to view team email addresses via the GET /api/v4/channels/{channel_id}/common_teams endpoint

CVE-2025-12559 Affected Github.com/mattermost/mattermost/server/v8 Versions

5 component(s)
Fixed Versions:
8.0.0-20251015091448-abbf01b9db4511.0.310.12.210.11.510.5.13
Product / Package Ecosystem Affected Versions Fixed Version
github.com/mattermost/mattermost/server/v8
golang/github.com/mattermost/mattermost/server/v8
Go
< 8.0.0-20251015091448-abbf01b9db45
8.0.0-20251015091448-abbf01b9db45
github.com/mattermost/mattermost-server
golang/github.com/mattermost/mattermost-server
Go
≥ 11.0.0
< 11.0.3
11.0.3
github.com/mattermost/mattermost-server
golang/github.com/mattermost/mattermost-server
Go
≥ 10.12.0
< 10.12.2
10.12.2
github.com/mattermost/mattermost-server
golang/github.com/mattermost/mattermost-server
Go
≥ 10.11.0
< 10.11.5
10.11.5
github.com/mattermost/mattermost-server
golang/github.com/mattermost/mattermost-server
Go
≥ 10.5.0
< 10.5.13
10.5.13

References

NVD — CVE-2025-12559 NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-12559
Github.com/mattermost/mattermost/server/v8 Source Repository REPOSITORY
https://github.com/mattermost/mattermost/pull/34110
Security Fix Commit FIX COMMIT
https://github.com/mattermost/mattermost/commit/5d8719042c1807da59ac8a821624eb01152d8495
Github.com/mattermost/mattermost/server/v8 Source Repository REPOSITORY
https://github.com/mattermost/mattermost
Security Fix Commit FIX COMMIT
https://github.com/mattermost/mattermost/commit/649aee8fa9184ca59bd66022a33b8f8918e413aa
Security Fix Commit FIX COMMIT
https://github.com/mattermost/mattermost/commit/7ccb62db7958abd6a4b21a06c5a4f5367a8f8b1f
Security Fix Commit FIX COMMIT
https://github.com/mattermost/mattermost/commit/9f54e5cdc3aef412945ff0e6a58338f7b549bdda
Security Fix Commit FIX COMMIT
https://github.com/mattermost/mattermost/commit/abbf01b9db45d1850eaf3701ea8362b910193ffd
Github.com/mattermost/mattermost/server/v8 Security Information SECURITY
https://mattermost.com/security-updates

Frequently Asked Questions

What is CVE-2025-12559?
CVE-2025-12559 is a security vulnerability in Github.com/mattermost/mattermost/server/v8 involving Mattermost fails to sanitize team email addresses under CWE-200: Exposure of Sensitive Information to an Unauthorized Actor.
Which Github.com/mattermost/mattermost/server/v8 versions are affected?
Affected versions include releases prior to 8.0.0-20251015091448-abbf01b9db45, 11.0.3, 10.12.2, 10.11.5, 10.5.13 across affected packages: github.com/mattermost/mattermost/server/v8, github.com/mattermost/mattermost-server.
What version fixes CVE-2025-12559?
Upgrading to 8.0.0-20251015091448-abbf01b9db45, 11.0.3, 10.12.2, 10.11.5, 10.5.13 (or the latest patched release for your respective branch) resolves the vulnerability.
Is github.com/mattermost/mattermost/server/v8 affected?
Yes, github.com/mattermost/mattermost/server/v8 is affected in releases prior to 8.0.0-20251015091448-abbf01b9db45. Upgrade your dependency to 8.0.0-20251015091448-abbf01b9db45 or later.
Is github.com/mattermost/mattermost-server affected?
Yes, github.com/mattermost/mattermost-server is affected in releases prior to 11.0.3, 10.12.2, 10.11.5, 10.5.13. Upgrade your dependency to 11.0.3, 10.12.2, 10.11.5, 10.5.13 or later.
What is the CVSS score of CVE-2025-12559?
CVE-2025-12559 has a CVSS v3.1 base score of 4.3 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N.
What CWE is associated with CVE-2025-12559?
CVE-2025-12559 is classified under CWE-200: Exposure of Sensitive Information to an Unauthorized Actor (The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.).
How can I check Go dependencies for CVE-2025-12559?
Run the dependency tree command: 'inspect dependencies for github.com/mattermost/mattermost/server/v8'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-4g87-9x45-cx2h",
  "modified" : "2025-12-01T23:57:02Z",
  "published" : "2025-11-27T18:30:25Z",
  "aliases" : [ "CVE-2025-12559" ],
  "summary" : "Mattermost fails to sanitize team email addresses",
  "details" : "Mattermost versions 11.0.x <= 11.0.2, 10.12.x <= 10.12.1, 10.11.x <= 10.11.4, 10.5.x <= 10.5.12 fail to sanitize team email addresses to be visible only to Team Admins, which allows any authenticated user to view team email addresses via the GET /api/v4/channels/{channel_id}/common_teams endpoint",
  "severity" : [ {
    "type" : "CVSS_V3",
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  } ],
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    },
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      "type" : "ECOSYSTEM",
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      } ]
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    },
    "ranges" : [ {
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  }, {
    "package" : {
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    },
    "ranges" : [ {
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    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/mattermost-server"
    },
    "ranges" : [ {
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        "introduced" : "10.5.0"
      }, {
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      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-12559"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/pull/34110"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/5d8719042c1807da59ac8a821624eb01152d8495"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/649aee8fa9184ca59bd66022a33b8f8918e413aa"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/7ccb62db7958abd6a4b21a06c5a4f5367a8f8b1f"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/9f54e5cdc3aef412945ff0e6a58338f7b549bdda"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/abbf01b9db45d1850eaf3701ea8362b910193ffd"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/mattermost/mattermost"
  }, {
    "type" : "WEB",
    "url" : "https://mattermost.com/security-updates"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-200" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-12-01T23:57:02Z",
    "nvd_published_at" : "2025-11-27T17:15:46Z"
  }
}