Understanding Remote code execution
What it is
Remote code execution is the top of the ladder: making the server run code you chose. It usually arrives through something more modest — an upload that lands somewhere executable, a template that evaluates input, a deserialization gadget, an injection that reaches a shell — escalated until the process does your bidding.
How you approach it
- Find the feature that treats your input as more than data — a file that gets executed, a template that gets evaluated, a value that reaches a shell.
- Get the smallest possible thing to run first: a value echoed back, a sleep you can time. Confirm execution before you build the payload.
- The flag is a file on the host that no web response is meant to include. Run the command that reads it.
How it gets fixed
A feature evaluated input that should have been inert, giving a path to command execution on the host. A minimal proof confirmed it before a full payload read the flag off the filesystem. The fix removes the evaluation entirely — no user input to a template engine, an interpreter or a shell.
Practise it
Every lab in the Remote code execution category drills exactly this. Start at Apprentice and work up.