The correct answer is B because the question directly describes a web application deserializing untrusted data, which is the classic condition for insecure deserialization. Deserialization is the process of converting serialized data back into an object or usable program structure. When an application accepts serialized data from an untrusted source and processes it without proper validation, integrity checking, or type restrictions, an attacker may manipulate the serialized object and influence application logic. In serious cases, this can result in remote code execution, privilege escalation, authentication bypass, or application takeover. The CEH web application security material maps this issue to OWASP web risks, where insecure deserialization is identified as a flaw that can lead to remote code execution attacks, which are among the most severe application impacts. SSTI involves server-side template injection, SQLi targets database queries, and XSS executes script in a user’s browser. Since the question specifically mentions untrusted deserialized data causing RCE, the precise flaw is insecure deserialization.