Log in Start free

Vulnerability · Published Mar 16, 2026 · Assigned by Mattermost

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

Medium 4.3

In plain English

A medium-severity incorrect authorization in Mattermost from Mattermost. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 14% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)4.3Medium
Exploit odds (30 days)0.2%top 85.9% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

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

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Gogithub.com/mattermost/mattermost-server11.2.3GHSA-xpvf-6qcc-9jqc
Gogithub.com/mattermost/mattermost-server5.3.2-0.20260107144005-c7f6efdfb035GHSA-xpvf-6qcc-9jqc
Gogithub.com/mattermost/mattermost-server10.11.11GHSA-xpvf-6qcc-9jqc
Gogithub.com/mattermost/mattermost-server11.3.1GHSA-xpvf-6qcc-9jqc
Gogithub.com/mattermost/mattermost-server10.11.11+incompatible, 11.2.3+incompatible, 11.3.1+incompatibleGO-2026-4749
Gogithub.com/mattermost/mattermost-server/v5no fix listedGO-2026-4749
Gogithub.com/mattermost/mattermost-server/v6no fix listedGO-2026-4749
Gogithub.com/mattermost/mattermost/server/v88.0.0-20260107144005-c7f6efdfb035GO-2026-4749
Gogithub.com/mattermost/mattermost/server/v88.0.0-20260107144005-c7f6efdfb035GHSA-xpvf-6qcc-9jqc

Affected products (as reported)

VendorProductVersions
Mattermost Mattermost 11.3.0 – through 11.3.011.2.0 – through 11.2.210.11.0 – through 10.11.10

Weakness: CWE-863 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

References