🛠️ Foundry CTF Template

A minimal and reusable Foundry project template for Ethereum CTF challenges following the Setup + Target pattern.

This template includes sample contracts, a Setup.sol wrapper, an optional Attacker.sol helper, and a Solidity script Solve.s.sol to automate the exploit process.

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📁 Project Layout

.
├── .env
├── .gitignore
├── docker-compose.yml
├── entrypoint.sh
├── Dockerfile
├── foundry.toml
├── remappings.txt
├── README.md
├── src
│   ├── Attacker.sol
│   ├── Creature.sol
│   └── Setup.sol
└── script
    └── Solve.s.sol

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📝 Environment Setup

.env – Configuration

PRIVATE_KEY=0x…      # Your EOA private key
SETUP_ADDRESS=0x…    # Deployed Setup contract address
CHAIN_ID=31337       # Chain ID of the network
RPC_URL=https://…    # RPC endpoint for the chain
FOUNDRY_DISABLE_NIGHTLY_WARNING=true

Load it with:

source .env        # Linux/macOS
.\.env             # Windows PowerShell

.gitignore

out/
cache/
lib/
.env

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⚒️ Foundry Configuration

foundry.toml

[profile.default]
solc_version = "0.8.15"
src = "src"
out = "out"
lib = "lib"
remappings = ["forge-std/=lib/forge-std/src/"]

remappings.txt

forge-std/=lib/forge-std/src/

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🚀 Getting Started (Without Docker)

1. Clone the template

git clone https://github.com/you/ctf-foundry-template.git
cd ctf-foundry-template

2. Install Foundry

curl -L https://foundry.paradigm.xyz | bash
foundryup

3. Install Dependencies

forge install foundry-rs/forge-std

4. Setup Environment

cp .env.example .env
# Then edit your values inside .env

5. Compile Contracts

source .env
forge clean
forge build

6. Run the Exploit

forge script script/Solve.s.sol:Solve \
  --rpc-url $RPC_URL \
  --private-key $PRIVATE_KEY \
 # --chain-id $CHAIN_ID \
  --broadcast \
  -vvvv

7. Fetch the Flag

: in HacktheBox sometime after solving challenge u can get a flag like this

curl http://<CTF-HOST>/flag

: Docker Ways is complex i recommend use the above style

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🐳 Docker Support

📦 Dockerfile

# 1. Base + Prereqs
FROM ghcr.io/foundry-rs/foundry:latest AS builder
USER root
WORKDIR /app

COPY foundry.toml remappings.txt ./
RUN mkdir -p lib && \
    git clone --depth 1 https://github.com/foundry-rs/forge-std lib/forge-std

COPY . .
RUN forge build --optimize

# 2. Runtime
FROM ghcr.io/foundry-rs/foundry:latest
WORKDIR /ctf

COPY --from=builder /app/lib ./lib
COPY --from=builder /app/out ./out
COPY --from=builder /app/src ./src
COPY --from=builder /app/script ./script
COPY entrypoint.sh ./

USER root
RUN chmod +x entrypoint.sh
USER forge

ENTRYPOINT ["./entrypoint.sh"]

entrypoint.sh

#!/usr/bin/env bash
set -e

if [ "$1" = "shell" ]; then
    echo "🛠️  Starting interactive shell..."
    exec bash
fi

echo "🚀 Running solver script..."
forge script script/Solve.s.sol:Solve \
    --rpc-url "$RPC_URL" \
    --private-key "$PRIVATE_KEY" \
    --chain-id "$CHAIN_ID" \
    --broadcast \
    -vvvv

echo "✅ Script execution completed successfully."

Make it executable:

chmod +x entrypoint.sh

Build and Run with Docker

# Build image
docker build -t ctf-template .

# Run solver script
docker run --rm -e RPC_URL=$RPC_URL \
                 -e PRIVATE_KEY=$PRIVATE_KEY \
                 -e CHAIN_ID=$CHAIN_ID \
                 ctf-template

# Start a shell
docker run --rm -it -e RPC_URL=$RPC_URL \
                      -e PRIVATE_KEY=$PRIVATE_KEY \
                      -e CHAIN_ID=$CHAIN_ID \
                      ctf-template shell

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🐋 Docker Compose

docker-compose.yml

version: "3.8"
services:
  ctf-template:
    build: .
    env_file:
      - .env
    volumes:
      - ./:/ctf
    command: ["${COMMAND:-}"]

Usage

# Build image
docker-compose build

# Run solver
docker-compose up --abort-on-container-exit

# Start a shell
COMMAND=shell docker-compose run --rm ctf-template

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🔧 Modifying the Template for a New CTF

1. Replace Creature.sol with your vulnerable target.
2. Update Setup.sol with the correct logic and deployed target.
3. Modify Solve.s.sol to reflect the new logic.
4. Optionally add helpers like Attacker.sol.
5. Use .env to plug in dynamic values.

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📚 References

• Foundry Book
• forge-std Docs
• cast CLI

This README generated by AI

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🧠 Tip: Fork this template for each challenge. Keep it clean. Hack smart.