Href Links as HTTP POST (complex DOM solution)

The earlier post, while easy to implement, has some well known security issues. Now lets get around them. First we’ll remove the FORM from the HTML itself, and instead build it dynamically and insert it into the BODY via the DOM and then submit it with JavaScript.

Again, if you’ve already implemented my prior solutions, this is just a small code refactor.

<html>
<head>
<title>Example FORM Post - DOM</title>
<script type="text/javascript">
/*
* Uses "location.replace()" vs. "location.href()" for all valid links.
* 'replace' has side-effect of 'restricting' back-button, or 'location'
* @param obj Object clicked
* @param x URL
*/
function xlinkObj(obj,url){
//Consider replacing w/ "return xlinkFrm(obj,url); " if you want POST behavior.
window.location.replace(uniqueUrl(url));
return false;
}
/*
* uses a FORM for the requested URL, could be POSTed!
* This is a simple solution, more complex solution COULD build the FORM and then parse attributes into INPUT's
* NOTE: you probably SHOULD NOT use this for external links, unless you intend for them to receive your params!
* @param obj Object clicked (NOT USED in this Example)
* @param x URL
*/
function xlinkFrm(obj,x){
var url=uniqueUrl(x);
var frmObj=xlinkFrmHelp(url);
if(frmObj!=null){
frmObj.submit();
}else{
alert('ERROR!');
}
return false;
}
/*
* Expects URL with queryString as param href
* @param x URL
* @return obj Object of the generated FORM
*/
function xlinkFrmHelp(x){
var rc=null;
try{
var ar = x.split("?");
var act = ar[0];
var str = ar[1];
var id="frm" + xmillis();
var oFORM=document.createElement("form");
oFORM.setAttribute("id",id);
oFORM.setAttribute("method","post");
oFORM.setAttribute("action",act);
if(str!=null){
var parms=str.split('&');
for(i=0; i < parms.length; i++){
var parm=parms[i];
var pair=parm.split('=');
var oINPUT=document.createElement("input");
oINPUT.setAttribute("type","hidden");
oINPUT.setAttribute("name",pair[0]);
oINPUT.setAttribute("value",pair[1]);
oFORM.appendChild(oINPUT);
}
}
var oBODY=document.getElementsByTagName("body")[0];
oBODY.appendChild(oFORM);
rc=oFORM;
}catch(e){
alert("Error"+e);
}
return rc;
}
/*
* generates a timestamp as a number
*/
function xmillis(){
return new Date().getTime();
}
/*
* adds timestamp to URLs to make them unique
* @param URL String
*/
function uniqueUrl(x){
return urlAppender(x,'time',xmillis());
}
/*
* helps to add parms to the url
* @param URL String
* @param aname String
* @param avalue String
*/
function urlAppender(x,aname,avalue){
var delim = "?";
if(x.indexOf("?") >=0) { delim = "&"; }
return x + delim + aname + '=' + avalue;
}
/*
* Abstracts "document.getElementById()" with appropriate error handling.
* @param id String
* @returns Object (NULL when not found!)
*/
function xgetHelper(id){
var obj = null;
try {
obj = document.getElementById(id);
} catch(z) {
var dummy=alert("Error:" + z);
}
return obj;
}
</script>
<a href="javascript:void(0);" onclick="return xlinkObj(this,'index.php');">REFRESH</a>
<a href="javascript:void(0);" onclick="return xlinkFrm(this,'index.php');">TEST-POST</a>
<a href="javascript:void(0);" onclick="return xlinkFrm(this,'index.php?a=b');">TEST-POST2</a>
<a href="javascript:void(0);" onclick="return xlinkFrm(this,'http://www.skotfred.com/hello');">TEST-XSS</a>
</body>
</html>

Cheers!

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