CVE-2026-6961: Github.com/mattermost/mattermost server Mattermost Doesn't Sanitize FileInfo.Name Received Vulnerability

HIGH
Advisory Identifier: GHSA-8qq9-cqj8-82w4
Share
CVSS 7.6
CWE-22
Published
Advisory Summary

CVE-2026-6961 is a HIGH (CVSS 7.6) mattermost doesn't sanitize fileinfo.name received vulnerability (CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')) affecting Github.com/mattermost/mattermost server libraries in the Go ecosystem. The issue involves mattermost doesn't sanitize fileinfo.name received from federated peers during shared channel file sync. Remediation is available by upgrading affected packages to version 11.6.1, 11.5.5, 10.11.17, 8.0.0-20260423180926-c021eeaff8f0.

CVE-2026-6961 at a Glance

CVE Identifier CVE-2026-6961
GHSA Identifier GHSA-8qq9-cqj8-82w4
Severity HIGH
CVSS v3.1 Base Score 7.6
CWE Classification CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Affected Product Github.com/mattermost/mattermost server
Package Ecosystem Go
Published Date
Last Updated

Security Impact

CVSS: 7.6

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:N/I:H/A:L).

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

How to Fix CVE-2026-6961

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: 8.0.0-20260423180926-c021eeaff8f0 
Upgrade github.com/mattermost/mattermost/server/v8 to 8.0.0-20260423180926-c021eeaff8f0
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-2026-6961, 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-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal'), where the product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. 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 sanitize FileInfo.Name received from federated peers during shared channel file sync, which allows an attacker who controls a federated server to write files to arbitrary locations within the target server's filestore via path traversal sequences in the filename field. Mattermost Advisory ID: MMSA-2026-00661

CVE-2026-6961 Affected Github.com/mattermost/mattermost server Versions

4 component(s)
Fixed Versions:
11.6.111.5.510.11.178.0.0-20260423180926-c021eeaff8f0
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
< 8.0.0-20260423180926-c021eeaff8f0
8.0.0-20260423180926-c021eeaff8f0

References

NVD — CVE-2026-6961 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-6961
Github.com/mattermost/mattermost server Source Repository REPOSITORY
https://github.com/mattermost/mattermost/pull/36255
Github.com/mattermost/mattermost server Source Repository REPOSITORY
https://github.com/mattermost/mattermost/pull/36253
Github.com/mattermost/mattermost server Source Repository REPOSITORY
https://github.com/mattermost/mattermost/pull/36252
Github.com/mattermost/mattermost server Source Repository REPOSITORY
https://github.com/mattermost/mattermost/pull/36251
Github.com/mattermost/mattermost server Source Repository REPOSITORY
https://github.com/mattermost/mattermost/pull/36223
Security Fix Commit FIX COMMIT
https://github.com/mattermost/mattermost/commit/c896a63dc44c2f9c081a0a15bfddc4e6eb50e753
Security Fix Commit FIX COMMIT
https://github.com/mattermost/mattermost/commit/c021eeaff8f003034ab40f82c552cc26a710a8fd
Security Fix Commit FIX COMMIT
https://github.com/mattermost/mattermost/commit/a9f3868e1eee9ec61855cd7277f39937385efffd
Security Fix Commit FIX COMMIT
https://github.com/mattermost/mattermost/commit/a0056ed68d95f64d7c4586985e7b7f16b96b3bec
Security Fix Commit FIX COMMIT
https://github.com/mattermost/mattermost/commit/61d68d2d6ee81a5919597d91c736c502d7156859
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
Github.com/mattermost/mattermost server Source Repository REPOSITORY
https://github.com/mattermost/mattermost

Frequently Asked Questions

What is CVE-2026-6961?
CVE-2026-6961 is a security vulnerability in Github.com/mattermost/mattermost server involving Mattermost doesn't sanitize FileInfo.Name received from federated peers during shared channel file sync under CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal').
Which Github.com/mattermost/mattermost server versions are affected?
Affected versions include releases prior to 11.6.1, 11.5.5, 10.11.17, 8.0.0-20260423180926-c021eeaff8f0 across affected packages: github.com/mattermost/mattermost-server, github.com/mattermost/mattermost/server/v8.
What version fixes CVE-2026-6961?
Upgrading to 11.6.1, 11.5.5, 10.11.17, 8.0.0-20260423180926-c021eeaff8f0 (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 8.0.0-20260423180926-c021eeaff8f0. Upgrade your dependency to 8.0.0-20260423180926-c021eeaff8f0 or later.
What is the CVSS score of CVE-2026-6961?
CVE-2026-6961 has a CVSS v3.1 base score of 7.6 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:N/I:H/A:L.
What CWE is associated with CVE-2026-6961?
CVE-2026-6961 is classified under CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') (The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.).
How can I check Go dependencies for CVE-2026-6961?
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-8qq9-cqj8-82w4",
  "modified" : "2026-08-24T21:45:52Z",
  "published" : "2026-06-12T18:31:59Z",
  "aliases" : [ "CVE-2026-6961" ],
  "summary" : "Mattermost doesn't sanitize FileInfo.Name received from federated peers during shared channel file sync",
  "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 sanitize FileInfo.Name received from federated peers during shared channel file sync, which allows an attacker who controls a federated server to write files to arbitrary locations within the target server's filestore via path traversal sequences in the filename field. Mattermost Advisory ID: MMSA-2026-00661",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:N/I:H/A:L"
  } ],
  "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" : "8.0.0-20260423180926-c021eeaff8f0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-6961"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/pull/36255"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/pull/36253"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/pull/36252"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/pull/36251"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/pull/36223"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/c896a63dc44c2f9c081a0a15bfddc4e6eb50e753"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/c021eeaff8f003034ab40f82c552cc26a710a8fd"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/a9f3868e1eee9ec61855cd7277f39937385efffd"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/a0056ed68d95f64d7c4586985e7b7f16b96b3bec"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/61d68d2d6ee81a5919597d91c736c502d7156859"
  }, {
    "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"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/mattermost/mattermost"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-24T21:45:51Z",
    "nvd_published_at" : "2026-06-12T17:16:27Z"
  }
}