libdebug

libdebug is an open source Python library for programmatic debugging of userland binary executables.

libdebug provides a comprehensive set of building blocks designed to facilitate the development of debugging tools for different purposes, including reverse engineering and exploitation. Build Your Own Debugger!

With libdebug you have full control of your debugged executable. With it you can:

• Access process memory and registers
• Control the execution flow of the process
• Handle and hijack syscalls
• Catch and hijack signals
• Interact with stdin, stdout, and stderr of the debugged process
• Debug multithreaded and multiprocess applications with ease
• Seamlessly switch to GDB for interactive analysis
• Debug on Linux systems based on AMD64, AArch64, and i386

When running the same executable multiple times, choosing efficient implementations can make the difference. For this reason, libdebug prioritizes performance.

Project Links

Homepage: https://libdebug.org
Documentation: https://docs.libdebug.org

Installation

python3 -m pip install libdebug

Please visit the build guide for more information on how to manually build libdebug from source.

Your first script

Now that you have libdebug installed, you can start using it in your scripts. Here is a simple example of how to use libdebug to debug a binary:

from libdebug import debugger

def my_callback(thread, bp) -> None:
	# This callback will be called when the breakpoint is hit
	print(f"RDX is {hex(thread.regs.rdx)}")
	print(f"This is the {bp.hit_count} time the breakpoint was hit")

d = debugger("./test")

# Start the process
# By default, the process will stop at the entry point
io = d.run()

my_breakpoint = d.breakpoint("function", hardware=True, file="binary")
my_callback_breakpoint = d.breakpoint("function2", callback=my_callback, file="binary")

# Continue the execution
d.cont()

# Interact with the process
io.sendline(b"Hello world!")
io.recvuntil(b"libdebug is like sushi")

# Print RAX. This will execute as soon as the process is stopped
print(f"RAX is {hex(d.regs.rax)}")

# Write to memory
d.memory[0x10ad, 8, "binary"] = b"Hello!\x00\x00"

# Continue the execution
d.cont()

The above script will run the binary test in the working directory and set two breakpoints: one at the function function and another at function2.

The first breakpoint has no callback, so it will just stop the execution and wait for your script to interact with the process. When the process stops at this breakpoint, you can read and write memory, access registers, and so on. In the example, we print the value of the RAX register and write a string to memory. Then, we continue the execution of the process.

The second breakpoint has a callback that will be called when the breakpoint is hit. Inside a callback, you can interact with the process, read and write memory, access registers, and so on. At the end of the callback, libdebug will automatically continue the execution of the process.

There is so much more that can be done with libdebug. Please read the documentation to find out more.

The cool stuff

libdebug offers many advanced features. Take a look at this script doing magic with signals:

from libdebug import debugger, libcontext

libcontext.terminal = ['tmux', 'splitw', '-h']

# Define signal catchers
def catcher_SIGUSR1(thread, catcher) -> None:
    thread.signal = 0x0
    print(f"SIGUSR1: Signal number {catcher}")

def catcher_SIGINT(thread, catcher) -> None:
    print(f"SIGINT: Signal number {catcher}")

def catcher_SIGPIPE(thread, catcher) -> None:
    print(f"SIGPIPE: Signal number {catcher}")

def handler_geteuid(thread, handler) -> None:
	thread.regs.rax = 0x0

# Initialize the debugger
d = debugger('/path/to/executable', continue_to_binary_entrypoint=False, aslr=False)

# Start the process
io = d.run()

# Register signal catchers
catcher1 = d.catch_signal("SIGUSR1", callback=catcher_SIGUSR1)
catcher2 = d.catch_signal("SIGINT", callback=catcher_SIGINT)
catcher3 = d.catch_signal("SIGPIPE", callback=catcher_SIGPIPE)

# Register signal hijackings
d.hijack_signal("SIGQUIT", "SIGTERM")
d.hijack_signal("SIGINT", "SIGPIPE", recursive=True)

# Define which signals to block
d.signals_to_block = ["SIGPOLL", "SIGIO", "SIGALRM"]

# Register a syscall handler
d.handle_syscall("geteuid", on_exit=handler_geteuid)

# Register a breakpoint
bp = d.breakpoint("function", hardware=True, file="binary")

# Continue execution
d.cont()

# Interact with the process
io.sendlineafter(b"libdebug is like provola", b"Hello world!")

# Wait for the process to stop
d.wait()

# Disable the catchers after execution
catcher1.disable()
catcher2.disable()
catcher3.disable()

# Register a new breakpoint
bp = d.breakpoint(0xdeadc0de, hardware=True)

d.cont()
d.wait()

d.gdb()

Auto Interrupt on Command

libdebug also allows you to make all commands execute as soon as possible, without having to wait for a stopping event. To enable this mode, you can use the auto_interrupt_on_command=True

from libdebug import debugger

d = debugger("/path/to/executable", auto_interrupt_on_command=True)

io = d.run()

bp = d.breakpoint("function", file="binary")

d.cont()

# Read shortly after the cont is issued
# The process is forcibly stopped to read the register
value = d.regs.rax
print(f"RAX is {hex(value)}")

system_offset = d.symbols.filter("system")[0].start
libc_base = d.maps.filter("libc")[0].base

system_address = libc_base + system_offset

d.memory[0x12ebe, 8, "libc"] = int.to_bytes(system_address, 8, "little")

d.cont()
d.wait()

# Here we should be at the breakpoint

# This value is read while the process is stopped at the breakpoint
ip_value = d.regs.rip

print(f"RIP is {hex(ip_value)}")

d.kill()

Attribution

We've published a poster on libdebug. If you use libdebug in your research, you can cite the associated poster paper:

@inproceedings{10.1145/3658644.3691391,
author = {Digregorio, Gabriele and Bertolini, Roberto Alessandro and Panebianco, Francesco and Polino, Mario},
title = {Poster: libdebug, Build Your Own Debugger for a Better (Hello) World},
year = {2024},
isbn = {9798400706363},
publisher = {Association for Computing Machinery},
address = {New York, NY, USA},
url = {https://doi.org/10.1145/3658644.3691391},
doi = {10.1145/3658644.3691391},
booktitle = {Proceedings of the 2024 on ACM SIGSAC Conference on Computer and Communications Security},
pages = {4976–4978},
numpages = {3},
keywords = {debugging, reverse engineering, software security},
location = {Salt Lake City, UT, USA},
series = {CCS '24}
}

If you intend to use libdebug in your projects, you can also cite the software using the following bibtex:

@software{libdebug_2024,
	title = {libdebug: {Build} {Your} {Own} {Debugger}},
	copyright = {MIT Licence},
	url = {https://libdebug.org},
	publisher = {libdebug.org},
	author = {Digregorio, Gabriele and Bertolini, Roberto Alessandro and Panebianco, Francesco and Polino, Mario},
	year = {2024},
	doi = {10.5281/zenodo.13151549},
}