CyberSecBulletin
CVE-2026-3473NVD status: Analyzed

Mattermost: Authorization Bypass Through User-Controlled Key

Published Updated By the CyberSecBulletin desk

CVE-2026-3473 is a high-severity authorization bypass through user-controlled key vulnerability in Mattermost, with a CVSS 3.1 base score of 7.1 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, without any action from a user. Affected Mattermost versions: 11.6.0 and earlier; 11.5.0 through 11.5.3; 11.4.0 through 11.4.4, and others listed below. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.15% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Mattermost Server to 10.11.15 or 11.4.5 or 11.5.4 or 11.6.1, whichever matches your release line, or a later version.
  2. Read the advisory on mattermost.com for workarounds and exact fixed builds.

Affected products and versions

VendorProductAffected versionsFixed in
MattermostMattermost11.6.0 and earlier; 11.5.0 through 11.5.3; 11.4.0 through 11.4.4; 10.11.0 through 10.11.14Not stated
MattermostMattermost Server10.11.0 up to, but not including, 10.11.15; 11.4.0 up to, but not including, 11.4.5; 11.5.0 up to, but not including, 11.5.4; 11.6.0 up to, but not including, 11.6.110.11.15, 11.4.5, 11.5.4, 11.6.1

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
LowA basic user account is enough.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
LowLimited modification of data is possible.
Availability
NoneAvailability is not affected.

Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 3.15.9MediumCNA (mattermost.com)
CVSS 3.17.1HighNVD

Official description

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate file ownership and access control, which allows an authenticated user to access and download files belonging to other users or teams via crafted Boards API requests using valid file IDs.. Mattermost Advisory ID: MMSA-2026-00620

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Authorization Bypass Through User-Controlled Key

The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.

How developers prevent this class of flaw

  • For each and every data access, ensure that the user has sufficient privilege to access the record that is being requested.
  • Make sure that the key that is used in the lookup of a specific user's record is not controllable externally by the user or that any tampering can be detected.
  • Use encryption in order to make it more difficult to guess other legitimate values of the key or associate a digital signature with the key so that the server can verify that there has been no tampering.

More Authorization Bypass Through User-Controlled Key vulnerabilities (CWE-639)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
  3. Record last changed materially (score, affected products, status or references).

References

Other vulnerabilities in Mattermost

All Mattermost vulnerabilities

Recent Authorization Bypass Through User-Controlled Key vulnerabilities

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