Shellcode injection is a technique in which an attacker places small machine-code payloads into another running process and makes that process execute the code. Instead of starting a new malicious program, the payload runs inside a trusted process, which can help it evade simple application controls and blend in with normal activity.
In cyber attacks, shellcode injection is often used to gain execution, load a larger implant, or move into another stage of malware without writing obvious files to disk. Defenders look for unusual memory writes, remote thread creation, process hollowing, and code running from nonstandard memory regions. Security tools that monitor process behavior, memory protections, and injection-related API calls can help detect it. In backdoors and loaders, shellcode injection is a common way to keep the intrusion flexible and harder to inspect.