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CVE-2026-104890— Kunstmaan CMS: MediaBundle extension blacklist bypass allows authenticated administrators to upload executable PHP files leading to remote code execution

Quick assessment

Affected
Kunstmaan KunstmaanBundlesCMS
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.

Kunstmaan CMS 是一个基于 Symfony 框架的开源内容管理系统。在 7.3.2 版本之前， 中的 方法对黑名单扩展名进行大小写敏感的检查，但在后续操作中将存储的扩展名统一转换为小写。因此，具有媒体访问权限的已认证后端用户可以通过上传混合大小写的可执行扩展名（例如 "PhP"）来绕过检查，该文件随后会被存储到可通过 Web 访问的媒体目录中，并以可执行的小写扩展名（如 "php"）存在。 此外，默认的黑名单遗漏了多种服务器可执行扩展名，导致攻击者可以利用相同的方式实现任意代码执行，即由 Web 服务器

CVSS 7.2 · High

Possible ATT&CK Techniques 1 AI

T1505.003 · Web Shell
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I. Basic Information for CVE-2026-104890

Vulnerability Information
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Vulnerability Title
Kunstmaan CMS: MediaBundle extension blacklist bypass allows authenticated administrators to upload executable PHP files leading to remote code execution
Source: CVE Program / CVE List V5
Vulnerability Description
Kunstmaan CMS is an open source content management system based on the Symfony framework. Prior to 7.3.2, src/Kunstmaan/MediaBundle/Helper/File/FileHandler.php performs the blacklisted_extensions check case-sensitively in FileHandler::getFilePath and lowercases the stored extension afterward. An authenticated backend user with media access can upload a mixed-case executable extension such as PHP that bypasses the check and is stored in the web-accessible media directory with an executable lowercase extension. The default blacklist also omits several server-executable extension types, allowing the same code-execution impact where the web server executes uploaded files. This issue is fixed in version 7.3.2.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
危险类型文件的不加限制上传
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Kunstmaan KunstmaanBundlesCMS < 7.3.1 -
kunstmaan bundles-cms < 7.3.1 -
kunstmaan media-bundle < 7.3.1 -

II. Public POCs for CVE-2026-104890

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III. Intelligence Information for CVE-2026-104890

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Other References for CVE-2026-104890 (3)

IV. Related Vulnerabilities

Same weakness: CWE-434

V. Comments for CVE-2026-104890

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