What can happen if processes are allowed to access each other's memory spaces?

Allowing processes to access each other's memory spaces can lead to significant security risks, primarily resulting in a loss of confidentiality. When processes share memory, one process may inadvertently or maliciously read sensitive data from another process's memory. This can include access to confidential user information, authentication tokens, or any sensitive data that a process is not authorized to see. Such vulnerabilities can be exploited by attackers to gain unauthorized access to information or manipulate data, leading to potential data breaches and other security incidents.

Maintaining clear boundaries between processes is essential for ensuring that sensitive information remains protected and that different processes operate securely without interference. In contrast, options such as increased performance or improved system reliability could be misleading since allowing memory access can introduce complexity and potential instability, rather than enhancing reliability. Similarly, data corruption prevention may not inherently arise from processes having mutual access to memory; rather, it can create additional risks for data integrity. Therefore, the primary concern when processes can access each other's memory spaces is the potential loss of confidentiality, making this the correct answer.