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CVE-2026-28736— Focalboard IDOR in file content endpoint allows cross-user file access (unsupported product, no fix)

Quick assessment

Affected
Mattermost Focalboard
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.

Focalboard是Mattermost Community开源的一个多语言、自托管的项目管理工具。 Focalboard 8.0版本存在安全漏洞，该漏洞源于提供上传文件时未验证文件所有权，可能导致知道受害者文件ID的经过身份验证的攻击者读取文件内容。

CVSS 4.3 · Medium EPSS 0.27% · P17

Possible ATT&CK Techniques 1 AI

T1530 · Data from Cloud Storage
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I. Basic Information for CVE-2026-28736

Vulnerability Information
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Vulnerability Title
Focalboard IDOR in file content endpoint allows cross-user file access (unsupported product, no fix)
Source: CVE Program / CVE List V5
Vulnerability Description
** UNSUPPORTED WHEN ASSIGNED ** Focalboard version 8.0 fails to validate file ownership when serving uploaded files. This allows an authenticated attacker who knows a victim's fileID to read the content of the file. NOTE: Focalboard as a standalone product is not maintained and no fix will be issued.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/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
Focalboard 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Focalboard是Mattermost Community开源的一个多语言、自托管的项目管理工具。 Focalboard 8.0版本存在安全漏洞，该漏洞源于提供上传文件时未验证文件所有权，可能导致知道受害者文件ID的经过身份验证的攻击者读取文件内容。
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 Focalboard 0 ~ 8.0 -

II. Public POCs for CVE-2026-28736

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III. Intelligence Information for CVE-2026-28736

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IV. Related Vulnerabilities

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

V. Comments for CVE-2026-28736

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