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CVE-2026-3473— Improper file ownership validation in the Boards API allows unauthorised file access

Quick assessment

Affected
Mattermost Mattermost
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Mattermost是美国Mattermost公司的一个开源协作平台。 Mattermost 11.6.0及之前的11.6.x版本、11.5.3及之前的11.5.x版本、11.4.4及之前的11.4.x版本和10.11.14及之前的10.11.x版本存在安全漏洞，该漏洞源于未能验证文件所有权和访问控制，可能导致认证用户通过特制的Boards API请求使用有效文件ID访问和下载属于其他用户或团队的文件。

CVSS 5.9 · Medium EPSS 0.15% · P5

Possible ATT&CK Techniques 1 AI

T1530 · Data from Cloud Storage

Affected Version Matrix 9

VendorProduct Version RangeStatus
Mattermost Mattermost 11.6.0≤ 11.6.0 affected
11.5.0≤ 11.5.3 affected
11.4.0≤ 11.4.4 affected
10.11.0≤ 10.11.14 affected
11.7.0 unaffected
11.6.1 unaffected
11.5.4 unaffected
11.4.5 unaffected
… +1 more rows
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I. Basic Information for CVE-2026-3473

Vulnerability Information
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Vulnerability Title
Improper file ownership validation in the Boards API allows unauthorised file access
Source: CVE Program / CVE List V5
Vulnerability 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: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
通过用户控制密钥绕过授权机制
Source: CVE Program / CVE List V5
Vulnerability Title
Mattermost 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mattermost是美国Mattermost公司的一个开源协作平台。 Mattermost 11.6.0及之前的11.6.x版本、11.5.3及之前的11.5.x版本、11.4.4及之前的11.4.x版本和10.11.14及之前的10.11.x版本存在安全漏洞，该漏洞源于未能验证文件所有权和访问控制，可能导致认证用户通过特制的Boards API请求使用有效文件ID访问和下载属于其他用户或团队的文件。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Mattermost Mattermost 11.6.0 ~ 11.6.0 -

II. Public POCs for CVE-2026-3473

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III. Intelligence Information for CVE-2026-3473

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Same Patch Batch · Mattermost · 2026-05-22 · 8 CVEs total

CVE-2026-5740 7.5 HIGH Unauthenticated WebSocket binary frame causes denial of service in Mattermost Server
CVE-2026-4635 6.5 MEDIUM Persistent notification timing attack causing server denial of service
CVE-2026-5755 6.5 MEDIUM Denial of service via crafted TIFF file upload
CVE-2026-28735 5.4 MEDIUM GitHub OAuth Scope Validation
CVE-2026-5308 4.9 MEDIUM Missing request body size limits on Zoom plugin HTTP endpoints
CVE-2026-4646 4.3 MEDIUM Insufficient input validation in GitHub plugin API causes denial of service
CVE-2026-3636 4.3 MEDIUM Sanitize team member data returned by API

IV. Related Vulnerabilities

Same product: Mattermost
Same vendor: Mattermost
Same weakness: CWE-639

V. Comments for CVE-2026-3473

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