bugku-web4

web4

打开网页源码，发现如下代码：

<script>
var p1 = '%66%75%6e%63%74%69%6f%6e%20%63%68%65%63%6b%53%75%62%6d%69%74%28%29%7b%76%61%72%20%61%3d%64%6f%63%75%6d%65%6e%74%2e%67%65%74%45%6c%65%6d%65%6e%74%42%79%49%64%28%22%70%61%73%73%77%6f%72%64%22%29%3b%69%66%28%22%75%6e%64%65%66%69%6e%65%64%22%21%3d%74%79%70%65%6f%66%20%61%29%7b%69%66%28%22%36%37%64%37%30%39%62%32%62';
var p2 = '%61%61%36%34%38%63%66%36%65%38%37%61%37%31%31%34%66%31%22%3d%3d%61%2e%76%61%6c%75%65%29%72%65%74%75%72%6e%21%30%3b%61%6c%65%72%74%28%22%45%72%72%6f%72%22%29%3b%61%2e%66%6f%63%75%73%28%29%3b%72%65%74%75%72%6e%21%31%7d%7d%64%6f%63%75%6d%65%6e%74%2e%67%65%74%45%6c%65%6d%65%6e%74%42%79%49%64%28%22%6c%65%76%65%6c%51%75%65%73%74%22%29%2e%6f%6e%73%75%62%6d%69%74%3d%63%68%65%63%6b%53%75%62%6d%69%74%3b';
eval(unescape(p1) + unescape('%35%34%61%61%32' + p2));
</script>

url解码后：

var p1 = 'function checkSubmit(){var a=document.getElementById("password");if("undefined"!=typeof a){if("67d709b2b';
var p2 = 'aa648cf6e87a7114f1"==a.value)return!0;alert("Error");a.focus();return!1}}document.getElementById("levelQuest").onsubmit=checkSubmit;';
eval(unescape(p1) + unescape('54aa2' + p2));

代码解析：
eval() 函数可计算某个字符串，并执行其中的的 JavaScript 代码。
unescape() 函数可对通过 escape() 编码的字符串进行解码。
escape() 函数可对字符串进行编码，这样就可以在所有的计算机上读取该字符串。
加号(+)拼接字符串，数字。

整理后代码如下：

function checkSubmit(){
    var a=document.getElementById("password");
    //获取ID名为password的文档元素，并赋给a
    if("undefined"!=typeof a){
    //判断a的类型是否undefined
        if("67d709b2b54aa2aa648cf6e87a7114f1"==a.value)
        //判断：a元素的value值是否为67d709b2b54aa2aa648cf6e87a7114f1
            return!0;
        alert("Error");
        //弹框：Error
        a.focus();
        //获得焦点时，改变背景颜色
        return!1
    }
}
document.getElementById("levelQuest").onsubmit=checkSubmit;
//获取ID值为levelQuest的文档元素，点击submit时执行checksubmit函数
//onsubmit：再点击submit时发生，若返回真提交表单

分析代码后，了解到表单的ID值为levelQuest，输入框的ID值为password，通过F12，修改网页元素为相应的值，在表单中提交67d709b2b54aa2aa648cf6e87a7114f1，拿到flag
p:考察Js，以及F12修改元素

转https://blog.csdn.net/w0ryitang/article/details/80112185

web4

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