Code Injection: What it is, how it leads to RCE, and how to prevent it

Code Injection

What it is

Code injection (often leading to remote code execution) is when attackers feed a program the kind of input it never expected—so it runs the attacker’s code instead of safe instructions. That “code” can be a script or DLL dropped after the first break-in. Our walkthrough 
code injection guide
.

How it works 

  • A vulnerable app trusts input (form fields, uploads, API calls).

  • The attacker crafts input that breaks out of normal handling.

  • Their code executes—downloading payloads, stealing data, or taking control.

What you might notice

  • Sudden processes you didn’t start; new services or tasks

  • Unusual outbound connections right after a form submit/upload

  • AV/EDR alerts about script hosts, PowerShell, or injected DLLs

If you suspect it 

  1. Isolate the host; preserve logs and memory.

  2. Block the offending URL/IP at WAF/firewall.

  3. Patch/disable the vulnerable feature; rotate secrets/keys.

  4. Hunt laterally for dropped payloads and persistence.

Prevent it

  • Validate and sanitize all inputs; treat uploads as untrusted.

  • Use allow-lists (what’s allowed) rather than block-lists.

  • Turn on WAF/Runtime protections (e.g., RASP) and strict content security.

  • Keep apps, libraries, and frameworks updated; avoid risky plugins.

  • Run services with least privilege; restrict script interpreters.

    Glossary (A–Z)

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