CVE-2026-4265 MEDIUM

CVE-2026-4265: Guest user can upload files without permission across teams

Vendor Mattermost
Product Mattermost
Weakness CWE-863 · Incorrect authorization
Published March 16, 2026
Last update March 16, 2026
View on NVD All CVEs

CVSS base score

4.3/10
Attack vector Network
Attack complexity Low
Privileges required Low
User interaction None
Confidentiality None
Integrity Low

CVSS vector

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

What the vulnerability does

01Description

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to validate team-specific upload_file permissions which allows a guest user to post files in channels where they lack upload_file permission via uploading files in a team where they have permission and reusing the file metadata in a POST request to a different team. Mattermost Advisory ID: MMSA-2025-00553

Key dates

02Disclosure timeline

March 16, 2026 CVE published
March 16, 2026 Record updated