FreeRDP is a free implementation of the Remote Desktop Protocol. Prior to version 3.20.0, a vulnerability exists in FreeRDP’s certificate handling code on Windows platforms. The function freerdp_certificate_data_hash_ uses the Microsoft-specific _snprintf function to format certificate cache filenames without guaranteeing NUL termination when truncation occurs.

According to Microsoft documentation, _snprintf does not append a terminating NUL byte if the formatted output exceeds the destination buffer size. If an attacker controls the hostname value (for example via server redirection or a crafted .rdp file), the resulting filename buffer may not be NUL-terminated. Subsequent string operations performed on this buffer may read beyond the allocated memory region, resulting in a heap-based out-of-bounds read.

In default configurations, the connection is typically terminated before sensitive data can be meaningfully exposed, but unintended memory read or a client crash may still occur under certain conditions. Version 3.20.0 has a patch for the issue.