# Course #664: UPX-UCL$ Fundamentals – Section 1: Introduction & Installation
## Introduction to UPX-UCL$
UPX (Ultimate Packer for eXecutables) is a powerful open-source executable packer that compresses executable files, allowing for smaller storage requirements and faster network transfers. UPX-UCL$ is an extension of UPX that utilizes the UCL compression library to enhance its capabilities.
UPX is widely used in the cybersecurity domain, especially in pentesting scenarios where executables need to be obfuscated to evade antivirus detection. Understanding how to effectively use UPX-UCL$ can drastically improve your pentesting toolkit.
In this section, we will cover the installation and configuration of UPX-UCL$ on Kali Linux, followed by step-by-step usage and real-world applications of this tool.
## Installation and Configuration on Kali Linux
### Prerequisites
Before we install UPX-UCL$, ensure that your Kali Linux environment is up-to-date. Open a terminal and execute:
"`bash
sudo apt update && sudo apt upgrade -y
"`
### Installing UPX-UCL$
UPX is included in the Kali Linux repositories. You can install it using the following command:
"`bash
sudo apt install upx-ucl
"`
To verify that UPX-UCL$ was installed successfully, run:
"`bash
upx –version
"`
You should see output similar to:
"`
UPX 3.95 2021-01-19 00:00:00
"`
This indicates that UPX is installed and ready for use.
### Configuration
While UPX does not require extensive configuration, you may want to customize your environment. You can create an alias or script to simplify running the commands. Open your `.bashrc` file:
"`bash
nano ~/.bashrc
"`
Add the following line:
"`bash
alias upx='upx –best –ultra-brute'
"`
This alias sets UPX to use the best compression method with ultra-brute options by default. Save the file and apply the changes:
"`bash
source ~/.bashrc
"`
## Step-by-Step Usage
### Basic Commands
Let’s go through some basic commands to understand how to use UPX-UCL$ effectively.
#### Compressing an Executable
To compress an executable, use the following command:
"`bash
upx input_file
"`
Replace `input_file` with the name of your executable. For example, if you have an executable named `example.exe`, you would use:
"`bash
upx example.exe
"`
#### Decompressing an Executable
To decompress a previously packed executable, use the `-d` flag:
"`bash
upx -d input_file
"`
This can be verified by executing the file again to ensure it runs correctly.
### Real-World Use Cases
UPX-UCL$ is particularly useful in the following pentesting scenarios:
1. **Executable Obfuscation**: To evade antivirus detection when transferring malware to different environments.
2. **Reducing File Size**: To optimize executables for network transfer or storage.
3. **Bait Creation**: To create decoy applications during penetration tests.
### Example Use Case: Obfuscating an Executable
Imagine you have a custom script or tool that you want to obfuscate before deploying it in a pentesting operation.
**Step 1**: Create an example executable. For demonstration purposes, we will use a simple "Hello World" program compiled into an executable format.
"`c
// hello.c
#include
int main() {
printf("Hello, World!n");
return 0;
}
"`
Compile the above code into an executable:
"`bash
gcc hello.c -o hello
"`
**Step 2**: Compress the executable using UPX:
"`bash
upx hello
"`
**Step 3**: Verify the compression:
"`bash
ls -lh hello
"`
You should see a reduced file size compared to before compression.
**Step 4**: Decompress the executable and verify its functionality:
"`bash
upx -d hello
./hello
"`
### Advanced Features
UPX-UCL$ has several options that allow for granular control over the packing process:
– `–best`: Use the best compression method.
– `–ultra-brute`: Attempts all possible combinations for maximum compression.
– `–force`: Overrides any warnings and forces the operation.
For a complete list of options, consult the UPX documentation or run:
"`bash
upx –help
"`
### External References
– UPX Official Documentation: [UPX Documentation](https://upx.github.io/)
– UCL Compression Library: [UCL](http://www.uclib.org/)
## Conclusion
In this section, we introduced you to UPX-UCL$, covering its installation, basic usage, and real-world applications in pentesting. Understanding how to effectively compress and obfuscate executables will enhance your capabilities as a white-hat pentester.
In the next section, we will delve deeper into advanced usage scenarios, including automation and integrating UPX-UCL$ into your pentesting workflow.
—
Made by pablo rotem / פבלו רותם