CVE-2026-4265 PUBLISHED

Guest user can upload files without permission across teams

Assigner: Mattermost
Reserved: 16.03.2026 Published: 16.03.2026 Updated: 16.03.2026

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

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
CVSS Score: 4.3

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	None
Privileges Required	Low	Integrity Impact	Low
User Interaction	None	Availability Impact	None

CVSS 3.1

Product Status

Vendor	Mattermost
Product	Mattermost
Versions	Default: unaffected affected from 11.3.0 to 11.3.0 (incl.) affected from 11.2.0 to 11.2.2 (incl.) affected from 10.11.0 to 10.11.10 (incl.) Version 11.4.0 is unaffected Version 11.3.1 is unaffected Version 11.2.3 is unaffected Version 10.11.11 is unaffected

Solutions

Update Mattermost to versions 11.4.0, 11.3.1, 11.2.3, 10.11.11 or higher.

Credits

0x7oda7123 finder

References

MMSA-2025-00553

Problem Types

CWE-863: Incorrect Authorization CWE