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CVE-2026-3473

Improper file ownership validation in the Boards API allows unauthorised file access

Published: May 22, 2026Updated: May 22, 2026 Sources: CVE List BDUCWE-639CWE-639: Authorization Bypass Through User-Controlled Key
NVD MITRE
5.9CVSSMEDIUM
EPSS Score
0.1%
Top 95.5%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

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

CVSS Vector Breakdown

AV:NAC:HPR:LUI:NS:UC:HI:LA:N
Exploitability
AV:NAttack Vector
Network
AC:HAttack Complexity
High
PR:LPrivileges Required
Low
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:HConfidentiality
High
I:LIntegrity
Low
A:NAvailability
None
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Weaknesses

CWE-639CWE-639: Authorization Bypass Through User-Controlled Key

Affected Products

MattermostMattermost
On-premWeb App
Communications / messaging-chat
MattermostMattermost Inc
On-premWeb App
Communications / messaging-chat
mattermostcommercialUSCommunications
mattermost inccommercialUSCommunicationsaka mattermost

Attack Graph

Products CVE Techniques Tactics

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Exploitability

Official Patch Available

MITRE ATT&CK

1 technique
Initial Access
View detailed technique mapping

References

https://mattermost.com/security-updates
mattermost.com
https://mattermost.com/security-updates&#13;
mattermost.com
https://feedly.com/cve/CVE-2026-3473&#13;
feedly.com
and 1 more references View all →

Timeline

Published
May 22, 2026
Last Updated
May 22, 2026

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