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The challenge to solve:

This is the code we know is on the server:

<?php
define('SYS_CON', 'dc877c9decfce360db824b8b2a385500816030be6e33dc770d77dffbf25addfe');
define('SYS_VER', 'b9e39ffdadb649289db6e601dc1e1f642cf6673c8908cdd24181a657cc68db8e');
define('SYS_AUT', '05a4d9e259fc3d11d997e521addb6be1cb8752e7f99339324f02d74f50f0254c');
//include("includes/anti_rfi.php"); //rfi is forbidden!!!!!
function x___1_k($l){$s=array();for($i=0;$i< strlen($l);$i++){array_push($s,substr($l,$i,1));}return $s;}
function x__3_h($k){$m="";foreach($k AS $x){$m.=$x;}return $m;}
$inc = $_GET['file'];
require_once(x__3_h(x___1_k($inc)).'.html');
?>

That is all we know. We are trying to accomplish Remote Code Execution. Using RFI or LFI to accomplish it is not allowed.

We also have a sample php.ini code that is installed on remote server:

;;;;;;;;;;;;;;;;
; File Uploads ;
;;;;;;;;;;;;;;;;

; Whether to allow HTTP file uploads.
; http://php.net/file-uploads
file_uploads = On

; Temporary directory for HTTP uploaded files (will use system default if not
; specified).
; http://php.net/upload-tmp-dir
;upload_tmp_dir =

; Maximum allowed size for uploaded files.
; http://php.net/upload-max-filesize
upload_max_filesize = 2M

;;;;;;;;;;;;;;;;;;
; Fopen wrappers ;
;;;;;;;;;;;;;;;;;;

; Whether to allow the treatment of URLs (like http:// or ftp://) as files.
; http://php.net/allow-url-fopen
allow_url_fopen = On

; Whether to allow include/require to open URLs (like http:// or ftp://) as files.
; http://php.net/allow-url-include
allow_url_include = On

; Define the anonymous ftp password (your email address). PHP's default setting
; for this is empty.
; http://php.net/from
;from="john@doe.com"

; Define the User-Agent string. PHP's default setting for this is empty.
; http://php.net/user-agent
;user_agent="PHP"

; Default timeout for socket based streams (seconds)
; http://php.net/default-socket-timeout
default_socket_timeout = 60

; If your scripts have to deal with files from Macintosh systems,
; or you are running on a Mac and need to deal with files from
; unix or win32 systems, setting this flag will cause PHP to
; automatically detect the EOL character in those files so that
; fgets() and file() will work regardless of the source of the file.
; http://php.net/auto-detect-line-endings
;auto_detect_line_endings = Off

;;;;;;;;;;;;;;;;;;;;;;
; Dynamic Extensions ;
;;;;;;;;;;;;;;;;;;;;;;

; If you wish to have an extension loaded automatically, use the following
; syntax:
;
;   extension=modulename.extension
;
; For example, on Windows:
;
;   extension=msql.dll
;
; ... or under UNIX:
;
;   extension=msql.so
;
; ... or with a path:
;
;   extension=/path/to/extension/msql.so
;
; If you only provide the name of the extension, PHP will look for it in its
; default extension directory.
;
; Windows Extensions
; Note that ODBC support is built in, so no dll is needed for it.
; Note that many DLL files are located in the extensions/ (PHP 4) ext/ (PHP 5)
; extension folders as well as the separate PECL DLL download (PHP 5).
; Be sure to appropriately set the extension_dir directive.
;
;extension=php_bz2.dll
;extension=php_curl.dll
;extension=php_dba.dll
;extension=php_exif.dll
;extension=php_fileinfo.dll
;extension=php_gd2.dll
;extension=php_gettext.dll
;extension=php_gmp.dll
;extension=php_intl.dll
;extension=php_imap.dll
;extension=php_interbase.dll
;extension=php_ldap.dll
;extension=php_mbstring.dll
;extension=php_ming.dll
;extension=php_mssql.dll
;extension=php_mysql.dll
;extension=php_mysqli.dll
;extension=php_oci8.dll      ; Use with Oracle 10gR2 Instant Client
;extension=php_oci8_11g.dll  ; Use with Oracle 11g Instant Client
;extension=php_openssl.dll
;extension=php_pdo_firebird.dll
;extension=php_pdo_mssql.dll
;extension=php_pdo_mysql.dll
;extension=php_pdo_oci.dll
;extension=php_pdo_odbc.dll
;extension=php_pdo_pgsql.dll
;extension=php_pdo_sqlite.dll
;extension=php_pgsql.dll
;extension=php_phar.dll
;extension=php_pspell.dll
;extension=php_shmop.dll
;extension=php_snmp.dll
;extension=php_soap.dll
;extension=php_sockets.dll
;extension=php_sqlite.dll
;extension=php_sqlite3.dll
;extension=php_sybase_ct.dll
;extension=php_tidy.dll
;extension=php_xmlrpc.dll
;extension=php_xsl.dll
;extension=php_zip.dll

extension="zip.so"

extension="sqlite.so"

extension="radius.so"

extension="pgsql.so"

; disabled in XAMPP 1.7.2 because incompatible with PHP 5.3.0
;extension="dbx.so"

extension="ming.so"

;extension="dio.so"

;extension="interbase.so"

; disabled in XAMPP 1.7.2 because incompatible with PHP 5.3.0
;extension="eaccelerator.so"
;eaccelerator.shm_size="16"
;eaccelerator.cache_dir="/opt/lampp/tmp/eaccelerator"
;eaccelerator.enable="1"
;eaccelerator.optimizer="1"
;eaccelerator.check_mtime="1"
;eaccelerator.debug="0"
;eaccelerator.filter=""
;eaccelerator.shm_max="0"
;eaccelerator.shm_ttl="0"
;eaccelerator.shm_prune_period="0"
;eaccelerator.shm_only="0"
;eaccelerator.compress="1"
;eaccelerator.compress_level="9"

;oci8mark


;;;;;;;;;;;;;;;;;;;
; Module Settings ;
;;;;;;;;;;;;;;;;;;;

[Date]
; Defines the default timezone used by the date functions
; http://php.net/date.timezone
date.timezone = Europe/Berlin

; http://php.net/date.default-latitude
;date.default_latitude = 31.7667

; http://php.net/date.default-longitude
;date.default_longitude = 35.2333

; http://php.net/date.sunrise-zenith
;date.sunrise_zenith = 90.583333

; http://php.net/date.sunset-zenith
;date.sunset_zenith = 90.583333

[filter]
; http://php.net/filter.default
;filter.default = unsafe_raw

; http://php.net/filter.default-flags
;filter.default_flags =

[iconv]
;iconv.input_encoding = ISO-8859-1
;iconv.internal_encoding = ISO-8859-1
;iconv.output_encoding = ISO-8859-1

[intl]
;intl.default_locale =

[sqlite]
; http://php.net/sqlite.assoc-case
;sqlite.assoc_case = 0

[sqlite3]
;sqlite3.extension_dir =

[Pcre]
;PCRE library backtracking limit.
; http://php.net/pcre.backtrack-limit
;pcre.backtrack_limit=100000

;PCRE library recursion limit.
;Please note that if you set this value to a high number you may consume all
;the available process stack and eventually crash PHP (due to reaching the
;stack size limit imposed by the Operating System).
; http://php.net/pcre.recursion-limit
;pcre.recursion_limit=100000

[Pdo]
; Whether to pool ODBC connections. Can be one of "strict", "relaxed" or "off"
; http://php.net/pdo-odbc.connection-pooling
;pdo_odbc.connection_pooling=strict

;pdo_odbc.db2_instance_name

[Pdo_mysql]
; If mysqlnd is used: Number of cache slots for the internal result set cache
; http://php.net/pdo_mysql.cache_size
pdo_mysql.cache_size = 2000

; Default socket name for local MySQL connects.  If empty, uses the built-in
; MySQL defaults.
; http://php.net/pdo_mysql.default-socket
pdo_mysql.default_socket=

[Phar]
; http://php.net/phar.readonly
;phar.readonly = On

; http://php.net/phar.require-hash
;phar.require_hash = On

;phar.cache_list =

[Syslog]
; Whether or not to define the various syslog variables (e.g. $LOG_PID,
; $LOG_CRON, etc.).  Turning it off is a good idea performance-wise.  In
; runtime, you can define these variables by calling define_syslog_variables().
; http://php.net/define-syslog-variables
define_syslog_variables  = Off

[mail function]
; For Win32 only.
; http://php.net/smtp
SMTP = localhost
; http://php.net/smtp-port
smtp_port = 25

; For Win32 only.
; http://php.net/sendmail-from
;sendmail_from = me@example.com

; For Unix only.  You may supply arguments as well (default: "sendmail -t -i").
; http://php.net/sendmail-path
;sendmail_path =

; Force the addition of the specified parameters to be passed as extra parameters
; to the sendmail binary. These parameters will always replace the value of
; the 5th parameter to mail(), even in safe mode.
;mail.force_extra_parameters =

; Add X-PHP-Originating-Script: that will include uid of the script followed by the filename
mail.add_x_header = On

; Log all mail() calls including the full path of the script, line #, to address and headers
;mail.log =










/////////////




End of php.ini file. The answer to the challenge is supposed to be in it...