Which of the following is a type of vulnerability for which no patch currently exists?

SQL injection is a well-known vulnerability that occurs when an attacker manipulates SQL queries to gain unauthorized access to a database. This type of vulnerability is widely understood and has established mitigation strategies, meaning that patches and defenses exist to address it.

A buffer overflow vulnerability arises when a program writes more data to a buffer than it can hold, leading to potential arbitrary code execution. While this is a significant security concern, there are various techniques and patches available to protect against buffer overflows, making it a manageable risk.

Firmware vulnerabilities refer to flaws in the software that is embedded in hardware devices, which can sometimes be patched. While firmware vulnerabilities can be severe, they are not a specific category of vulnerability without patches, as manufacturers often release updates to fix these issues.