CVE-2026-3433: Github.com/mattermost/mattermost server Mattermost Doesn't Restrict Role_updated Websocket Vulnerability

Q: What is CVE-2026-3433?

CVE-2026-3433 is a security vulnerability in Github.com/mattermost/mattermost server involving Mattermost doesn't restrict role_updated websocket event broadcasts to members of the affected team or channel under CWE-200: Exposure of Sensitive Information to an Unauthorized Actor.

Q: Which Github.com/mattermost/mattermost server versions are affected?

Affected versions include releases prior to 11.6.1, 11.5.5, 10.11.17, 8.0.0-20260504071740-9408b98025d7 across affected packages: github.com/mattermost/mattermost-server, github.com/mattermost/mattermost/server/v8.

Q: What version fixes CVE-2026-3433?

Upgrading to 11.6.1, 11.5.5, 10.11.17, 8.0.0-20260504071740-9408b98025d7 (or the latest patched release for your respective branch) resolves the vulnerability.

Q: Is github.com/mattermost/mattermost-server affected?

Yes, github.com/mattermost/mattermost-server is affected in releases prior to 11.6.1, 11.5.5, 10.11.17. Upgrade your dependency to 11.6.1, 11.5.5, 10.11.17 or later.

Q: Is github.com/mattermost/mattermost/server/v8 affected?

Yes, github.com/mattermost/mattermost/server/v8 is affected in releases prior to 8.0.0-20260504071740-9408b98025d7. Upgrade your dependency to 8.0.0-20260504071740-9408b98025d7 or later.

Q: What is the CVSS score of CVE-2026-3433?

CVE-2026-3433 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.

Q: What CWE is associated with CVE-2026-3433?

CVE-2026-3433 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.).

Q: How can I check Go dependencies for CVE-2026-3433?

Run the dependency tree command: 'inspect dependencies for github.com/mattermost/mattermost-server'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.

MODERATE

Advisory Identifier: GHSA-rp4v-qc77-phm4

CVSS 4.3

CWE-200

Published 2026-06-12

Advisory Summary

CVE-2026-3433 is a MODERATE (CVSS 4.3) mattermost doesn't restrict role_updated websocket vulnerability (CWE-200: Exposure of Sensitive Information to an Unauthorized Actor) affecting Github.com/mattermost/mattermost server libraries in the Go ecosystem. The issue involves mattermost doesn't restrict role_updated websocket event broadcasts to members of the affected team or channel. Remediation is available by upgrading affected packages to version 11.6.1, 11.5.5, 10.11.17, 8.0.0-20260504071740-9408b98025d7.

CVE-2026-3433 at a Glance

CVE Identifier CVE-2026-3433

GHSA Identifier GHSA-rp4v-qc77-phm4

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

Package Ecosystem Go

Published Date 2026-06-12

Last Updated 2026-08-24

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-2026-3433

To remediate this vulnerability, upgrade all affected Github.com/mattermost/mattermost server 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 fixed: 11.6.1

Upgrade github.com/mattermost/mattermost-server to 11.6.1

github.com/mattermost/mattermost-server fixed: 11.5.5

Upgrade github.com/mattermost/mattermost-server to 11.5.5

github.com/mattermost/mattermost-server fixed: 10.11.17

Upgrade github.com/mattermost/mattermost-server to 10.11.17

github.com/mattermost/mattermost/server/v8 fixed: 8.0.0-20260504071740-9408b98025d7

Upgrade github.com/mattermost/mattermost/server/v8 to 8.0.0-20260504071740-9408b98025d7

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

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-3433, inspect your project dependencies for Github.com/mattermost/mattermost server:

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

Analyze the terminal output to locate any version of Github.com/mattermost/mattermost server in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 11.6.1), 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, 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 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to restrict role_updated websocket event broadcasts to members of the affected team or channel, which allows an authenticated attacker with guest-level access to observe permission scheme change notifications for private teams they are not a member of via the websocket connection. Mattermost Advisory ID: MMSA-2026-00616

CVE-2026-3433 Affected Github.com/mattermost/mattermost server Versions

4 component(s)

Fixed Versions:

11.6.111.5.510.11.178.0.0-20260504071740-9408b98025d7

Product / Package	Ecosystem	Affected Versions	Fixed Version
github.com/mattermost/mattermost-server golang/github.com/mattermost/mattermost-server	Go	≥ 11.6.0 < 11.6.1 All 1 versions 11.6.0	11.6.1
github.com/mattermost/mattermost-server golang/github.com/mattermost/mattermost-server	Go	≥ 11.5.0 < 11.5.5	11.5.5
github.com/mattermost/mattermost-server golang/github.com/mattermost/mattermost-server	Go	≥ 10.11.0 < 10.11.17	10.11.17
github.com/mattermost/mattermost/server/v8 golang/github.com/mattermost/mattermost/server/v8	Go	≥ 8.0.0-20250731163400-5b955468ea1e < 8.0.0-20260504071740-9408b98025d7	8.0.0-20260504071740-9408b98025d7

References

NVD — CVE-2026-3433 NVD

https://nvd.nist.gov/vuln/detail/CVE-2026-3433

Github.com/mattermost/mattermost server Source Repository REPOSITORY

https://github.com/mattermost/mattermost/pull/35497

Github.com/mattermost/mattermost server Source Repository REPOSITORY

https://github.com/mattermost/mattermost/pull/36256

Github.com/mattermost/mattermost server Source Repository REPOSITORY

https://github.com/mattermost/mattermost/pull/36257

Github.com/mattermost/mattermost server Source Repository REPOSITORY

https://github.com/mattermost/mattermost/pull/36341

Security Fix Commit FIX COMMIT

https://github.com/mattermost/mattermost/commit/0a0ab0d54d899d308bd1352cc577036917500318

Security Fix Commit FIX COMMIT

https://github.com/mattermost/mattermost/commit/7425c6817bf244f976c729f8a73cecac8039a1e1

Security Fix Commit FIX COMMIT

https://github.com/mattermost/mattermost/commit/9408b98025d7364d7dfe7cdb28fcd109b1b595a6

Security Fix Commit FIX COMMIT

https://github.com/mattermost/mattermost/commit/a30a331a29b9766d46716d4252056d7b74e66da0

Github.com/mattermost/mattermost server Source Repository REPOSITORY

https://github.com/mattermost/mattermost

Github.com/mattermost/mattermost server Release RELEASE

https://github.com/mattermost/mattermost/releases/tag/v10.11.16

Github.com/mattermost/mattermost server Release RELEASE

https://github.com/mattermost/mattermost/releases/tag/v11.5.5

Github.com/mattermost/mattermost server Release RELEASE

https://github.com/mattermost/mattermost/releases/tag/v11.6.2

Github.com/mattermost/mattermost server Release RELEASE

https://github.com/mattermost/mattermost/releases/tag/v11.7.0

Github.com/mattermost/mattermost server Security Information SECURITY

https://mattermost.com/security-updates

Frequently Asked Questions

What is CVE-2026-3433?

CVE-2026-3433 is a security vulnerability in Github.com/mattermost/mattermost server involving Mattermost doesn't restrict role_updated websocket event broadcasts to members of the affected team or channel under CWE-200: Exposure of Sensitive Information to an Unauthorized Actor.

Which Github.com/mattermost/mattermost server versions are affected?

Affected versions include releases prior to 11.6.1, 11.5.5, 10.11.17, 8.0.0-20260504071740-9408b98025d7 across affected packages: github.com/mattermost/mattermost-server, github.com/mattermost/mattermost/server/v8.

What version fixes CVE-2026-3433?

Upgrading to 11.6.1, 11.5.5, 10.11.17, 8.0.0-20260504071740-9408b98025d7 (or the latest patched release for your respective branch) resolves the vulnerability.

Is github.com/mattermost/mattermost-server affected?

Yes, github.com/mattermost/mattermost-server is affected in releases prior to 11.6.1, 11.5.5, 10.11.17. Upgrade your dependency to 11.6.1, 11.5.5, 10.11.17 or later.

Is github.com/mattermost/mattermost/server/v8 affected?

Yes, github.com/mattermost/mattermost/server/v8 is affected in releases prior to 8.0.0-20260504071740-9408b98025d7. Upgrade your dependency to 8.0.0-20260504071740-9408b98025d7 or later.

What is the CVSS score of CVE-2026-3433?

CVE-2026-3433 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-2026-3433?

CVE-2026-3433 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-2026-3433?

Run the dependency tree command: 'inspect dependencies for github.com/mattermost/mattermost-server'. 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-rp4v-qc77-phm4",
  "modified" : "2026-08-24T21:30:50Z",
  "published" : "2026-06-12T18:31:59Z",
  "aliases" : [ "CVE-2026-3433" ],
  "summary" : "Mattermost doesn't restrict role_updated websocket event broadcasts to members of the affected team or channel",
  "details" : "Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to restrict role_updated websocket event broadcasts to members of the affected team or channel, which allows an authenticated attacker with guest-level access to observe permission scheme change notifications for private teams they are not a member of via the websocket connection. Mattermost Advisory ID: MMSA-2026-00616",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/mattermost-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "11.6.0"
      }, {
        "fixed" : "11.6.1"
      } ]
    } ],
    "versions" : [ "11.6.0" ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/mattermost-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "11.5.0"
      }, {
        "fixed" : "11.5.5"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 11.5.4"
    }
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/mattermost-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "10.11.0"
      }, {
        "fixed" : "10.11.17"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 10.11.15"
    }
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/mattermost/server/v8"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "8.0.0-20250731163400-5b955468ea1e"
      }, {
        "fixed" : "8.0.0-20260504071740-9408b98025d7"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-3433"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/pull/35497"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/pull/36256"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/pull/36257"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/pull/36341"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/0a0ab0d54d899d308bd1352cc577036917500318"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/7425c6817bf244f976c729f8a73cecac8039a1e1"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/9408b98025d7364d7dfe7cdb28fcd109b1b595a6"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/a30a331a29b9766d46716d4252056d7b74e66da0"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/mattermost/mattermost"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/releases/tag/v10.11.16"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/releases/tag/v11.5.5"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/releases/tag/v11.6.2"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/releases/tag/v11.7.0"
  }, {
    "type" : "WEB",
    "url" : "https://mattermost.com/security-updates"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-200" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-24T21:30:50Z",
    "nvd_published_at" : "2026-06-12T17:16:22Z"
  }
}

CVSS V3

4.3 MODERATE

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)

Vector String

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

Advisory Metadata

Source ID: GHSA-rp4v-qc77-phm4
Schema Version: 1.4.0
Published: 2026-06-12 18:31
Last Modified: 2026-08-24 21:30
Database Record File: advisories/github-reviewed/2026/06/GHSA-rp4v-qc77-phm4/GHSA-rp4v-qc77-phm4.json