Is CVE-2026-4265 actively exploited?

CVE-2026-4265 has no public evidence of in-the-wild exploitation as of 2026-03-18.

What is the CVSS score for CVE-2026-4265?

CVE-2026-4265 has a CVSS score of 4.3 (MEDIUM severity). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N.

How do I patch CVE-2026-4265?

Patch guidance is available from mattermost security advisories. CVEDatabase generates AI-assisted remediation guidance on demand for CVE-2026-4265.

CVE-2026-4265 - remediation guidance & executive summary

Q: Which products are affected by CVE-2026-4265?

3 products: mattermost mattermost server, mattermost mattermost server, mattermost mattermost server.

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

CVSS Metrics

Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
Attack Vector: network
Complexity: low
Privileges: low
User Action: none
Scope: unchanged
Confidentiality: none
Integrity: low
Availability: none
Weaknesses: CWE-863 · Incorrect Authorization

Metadata

Primary Vendor: MATTERMOST
Published: 3/16/2026
Last Modified: 3/18/2026
Source: NIST NVD
Note: Verify all details with official vendor sources before applying patches.

Affected Products

mattermost : mattermost_servermattermost : mattermost_servermattermost : mattermost_server

Remediation Guidance

Executive Summary

Cite this page

CVE-2026-4265. CVEDatabase.com. Retrieved 1 May 2026. https://cvedatabase.com/cve/CVE-2026-4265

View on NIST NVD

CVE-2026-4265 vulnerability