---
id: CVE-2026-96259
title: >-
  Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10,
  11.10.x <= 11.10.1 fail to apply the internal-connection filter to OAuth
  endpoint requests, which allows a System Administrator to make the server
  issue requests …
summary: >-
  Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10,
  11.10.x <= 11.10.1 fail to apply the internal-connection filter to OAuth
  endpoint requests, which allows a System Administrator to make the server
  issue requests …
severity: medium
cvss: 5.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:L/I:L/A:N'
cwe:
  - CWE-918
vendor: Mattermost
product: Mattermost
affected:
  - Mattermost >= 11.9.0 <= 11.9.1
  - Mattermost >= 11.8.0 <= 11.8.5
  - Mattermost >= 11.7.0 <= 11.7.10
  - Mattermost >= 11.10.0 <= 11.10.1
published: '2026-09-22'
updated: '2026-09-23'
sourceUpdated: '2026-09-23T18:17:31.543'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-96259'
references:
  - url: 'https://mattermost.com/security-updates'
    label: responsibledisclosure@mattermost.com
tags:
  - nvd
  - cve.org
epss: 0.00255
epssPercentile: 0.15166
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-23T13:10:28.219588Z'
ingestedAt: '2026-09-22T21:11:40.323Z'
---

## Overview

Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to apply the internal-connection filter to OAuth endpoint requests, which allows a System Administrator to make the server issue requests to internal network addresses and read the responses via the configured OAuth token and userinfo endpoints.. Mattermost Advisory ID: MMSA-2026-00776

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.