Description

Editor Arbitrary File Upload in Fluent Boards Pro <= 2.0.11 versions.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "9.1",
  "pubDate": "2026-08-27T10:16:37.383Z",
  "pubdate": "2026-08-27T10:16:37.383Z",
  "executiveSummary": "Fluent Boards Pro versions 2.0.11 and below contain an arbitrary file upload vulnerability within the editor component. This security flaw allows an authenticated attacker to bypass file type validation mechanisms, enabling the upload of arbitrary files, including executable scripts such as PHP, to the server.\nThe impact of this vulnerability is critical, potentially leading to Remote Code Execution (RCE) on the underlying web server. By successfully uploading a malicious payload, an attacker could gain full control over the application, execute arbitrary commands, compromise sensitive data, or establish persistent backdoors within the environment.\nThe vulnerability is primarily accessible to authenticated users with sufficient privileges to access the board editor. Successful exploitation requires knowledge of the file upload endpoint and the ability to bypass restricted file extension filtering. The flaw exists due to inadequate sanitization and insufficient validation of uploaded file extensions or MIME types during the save or update operations within the component.\nOrganizations using affected versions of Fluent Boards Pro are at risk of significant compromise if an attacker with low-to-medium level administrative access is present, or if user-controlled access to the editor is misconfigured.",
  "technicalDetails": "The vulnerability resides in the file handling logic of the Fluent Boards Pro editor component. The application fails to strictly enforce server-side validation for uploaded files, specifically regarding the file extension and content type. This allows an attacker to inject files that do not align with intended media or document formats, such as PHP scripts or other server-side executables.\nThe root cause is an insecure implementation of the file upload mechanism, which relies on client-side validation or insufficient server-side filtering. In affected versions (<= 2.0.11), the backend does not verify that the uploaded file matches an expected whitelist of safe file types, nor does it sanitize the filename or move the uploaded file to a non-executable directory.\nThe attack flow typically follows these steps: 1) The attacker authenticates as a user with access to the board editor functionality. 2) The attacker initiates an upload request through the vulnerable component's interface. 3) The attacker intercepts the HTTP request and replaces or injects a malicious file (e.g., a webshell.php). 4) Due to the lack of strict extension verification, the application accepts the malicious file and stores it in a publicly accessible directory or a directory that the web server processes.\nOnce the file is uploaded, the attacker can execute the code by navigating directly to the file's path via a standard web browser request. Because the server processes these files, the attacker achieves arbitrary command execution within the context of the web server process (e.g., www-data).\nPost-exploitation, the attacker can leverage this execution to escalate privileges, dump the application database, pivot into the internal network, or deploy persistent malware. The vulnerability is highly critical because it does not require complex infrastructure manipulation, only the ability to reach the upload endpoint and provide a payload that the web server will interpret as code. The absence of server-side sanitization remains the primary technical vector allowing this bypass."
}