CVE-2025-13821: Github.com/mattermost/mattermost/server/v8 Mattermost Fails To Sanitize Sensitive Vulnerability

MODERATE
Advisory Identifier: GHSA-pp9j-pf5c-659x
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CVSS 5.7
CWE-200
Published
Advisory Summary

CVE-2025-13821 is a MODERATE (CVSS 5.7) mattermost fails to sanitize sensitive 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 sensitive data in websocket messages. Remediation is available by upgrading affected packages to version 8.0.0-20251210191531-cd17b61de41b, 5.3.2-0.20251210191531-cd17b61de41b.

CVE-2025-13821 at a Glance

CVE Identifier CVE-2025-13821
GHSA Identifier GHSA-pp9j-pf5c-659x
Severity MODERATE
CVSS v3.1 Base Score 5.7
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: 5.7

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:R/S:U/C:H/I:N/A:N).

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

How to Fix CVE-2025-13821

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: 8.0.0-20251210191531-cd17b61de41b 
Upgrade github.com/mattermost/mattermost/server/v8 to 8.0.0-20251210191531-cd17b61de41b
github.com/mattermost/mattermost-server fixed: Latest secure release 
Upgrade github.com/mattermost/mattermost-server to Latest secure release
github.com/mattermost/mattermost-server fixed: Latest secure release 
Upgrade github.com/mattermost/mattermost-server to Latest secure release
github.com/mattermost/mattermost-server fixed: Latest secure release 
Upgrade github.com/mattermost/mattermost-server to Latest secure release
github.com/mattermost/mattermost-server fixed: 5.3.2-0.20251210191531-cd17b61de41b 
Upgrade github.com/mattermost/mattermost-server to 5.3.2-0.20251210191531-cd17b61de41b
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-2025-13821, 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 8.0.0-20251210191531-cd17b61de41b), 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 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 fail to sanitize sensitive data in WebSocket messages which allows authenticated users to exfiltrate password hashes and MFA secrets via profile nickname updates or email verification events. Mattermost Advisory ID: MMSA-2025-00560

CVE-2025-13821 Affected Github.com/mattermost/mattermost/server/v8 Versions

5 component(s)
Fixed Versions:
8.0.0-20251210191531-cd17b61de41b5.3.2-0.20251210191531-cd17b61de41b
Product / Package Ecosystem Affected Versions Fixed Version
github.com/mattermost/mattermost/server/v8
golang/github.com/mattermost/mattermost/server/v8
Go
< 8.0.0-20251210191531-cd17b61de41b
8.0.0-20251210191531-cd17b61de41b
github.com/mattermost/mattermost-server
golang/github.com/mattermost/mattermost-server
Go
≥ 11.1.0
github.com/mattermost/mattermost-server
golang/github.com/mattermost/mattermost-server
Go
≥ 10.11.0
github.com/mattermost/mattermost-server
golang/github.com/mattermost/mattermost-server
Go
≥ 11.2.0
github.com/mattermost/mattermost-server
golang/github.com/mattermost/mattermost-server
Go
< 5.3.2-0.20251210191531-cd17b61de41b
5.3.2-0.20251210191531-cd17b61de41b

References

NVD — CVE-2025-13821 NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-13821
Security Fix Commit FIX COMMIT
https://github.com/mattermost/mattermost/commit/cd17b61de41bf0a49b524bb91ce0bbe859e5a100
Github.com/mattermost/mattermost/server/v8 Source Repository REPOSITORY
https://github.com/mattermost/mattermost
Github.com/mattermost/mattermost/server/v8 Security Information SECURITY
https://mattermost.com/security-updates

Frequently Asked Questions

What is CVE-2025-13821?
CVE-2025-13821 is a security vulnerability in Github.com/mattermost/mattermost/server/v8 involving Mattermost fails to sanitize sensitive data in WebSocket messages 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 8.0.0-20251210191531-cd17b61de41b, 5.3.2-0.20251210191531-cd17b61de41b across affected packages: github.com/mattermost/mattermost/server/v8, github.com/mattermost/mattermost-server.
What version fixes CVE-2025-13821?
Upgrading to 8.0.0-20251210191531-cd17b61de41b, 5.3.2-0.20251210191531-cd17b61de41b (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 8.0.0-20251210191531-cd17b61de41b. Upgrade your dependency to 8.0.0-20251210191531-cd17b61de41b or later.
Is github.com/mattermost/mattermost-server affected?
Yes, github.com/mattermost/mattermost-server is affected in releases prior to Latest secure release, 5.3.2-0.20251210191531-cd17b61de41b. Upgrade your dependency to Latest secure release, 5.3.2-0.20251210191531-cd17b61de41b or later.
What is the CVSS score of CVE-2025-13821?
CVE-2025-13821 has a CVSS v3.1 base score of 5.7 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:N/A:N.
What CWE is associated with CVE-2025-13821?
CVE-2025-13821 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-2025-13821?
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-pp9j-pf5c-659x",
  "modified" : "2026-02-19T19:35:11Z",
  "published" : "2026-02-16T12:30:25Z",
  "aliases" : [ "CVE-2025-13821" ],
  "summary" : "Mattermost fails to sanitize sensitive data in WebSocket messages",
  "details" : "Mattermost versions 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 fail to sanitize sensitive data in WebSocket messages which allows authenticated users to exfiltrate password hashes and MFA secrets via profile nickname updates or email verification events. Mattermost Advisory ID: MMSA-2025-00560",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:N/A:N"
  } ],
  "affected" : [ {
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    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "8.0.0-20251210191531-cd17b61de41b"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/mattermost-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "11.1.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "< 11.1.3"
    }
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/mattermost-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "10.11.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "< 10.11.10"
    }
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/mattermost-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "11.2.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "< 11.2.2"
    }
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/mattermost-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "5.3.2-0.20251210191531-cd17b61de41b"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-13821"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/cd17b61de41bf0a49b524bb91ce0bbe859e5a100"
  }, {
    "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" : "2026-02-19T19:35:11Z",
    "nvd_published_at" : "2026-02-16T12:16:21Z"
  }
}