CVE-2020-9471

CVE-2020-9471 is a vulnerability in Umbraco Cloud 8.5.3, an open-source .NET content management system. The issue resides in the Install Packages functionality, which does not adequately validate or restrict the types of files that can be uploaded by an authenticated user. This flaw allows a user with valid credentials to upload and execute arbitrary code on the server [1].

The attack vector requires the attacker to have valid authentication to the Umbraco backoffice. No other special privileges are necessary. By crafting a malicious package file that contains executable code (e.g., a .NET assembly or other script file), the attacker can upload it through the package installation interface. Once uploaded, the malicious file can be executed in the context of the web server, achieving remote code execution [1].

Successful exploitation grants the attacker the ability to execute arbitrary code on the underlying server. Depending on the server's configuration, this could lead to full compromise of the Umbraco instance, access to sensitive data, and lateral movement within the hosting environment. The impact is severe as it moves from authenticated file upload to complete system control [1].

At the time of disclosure, Umbraco released updates to address this vulnerability. The official recommendation is to upgrade to a patched version of Umbraco CMS. The project's source code is available on GitHub, and administrators should verify they are running a version that is not affected by this issue [2].