The vulnerability description explicitly identifies SaveFilesToDisk in BlogController.cs as the source of improper input validation. The function decodes() base64 data and writes it to disk using a filename derived from user-controlled input (the 'data-filename' attribute). While the current GitHub code shows an allowed extensions check, the vulnerability exists in versions <=1.0.3 where this validation was either absent or insufficient. Attackers could bypass checks by manipulating the filename extension, enabling ASPX file uploads. The link to CVE-2019-9845 and the exploit analysis confirms this mechanism.