XCTF-NaNNaNNaNNaN-Batman

下载附件，打开后发现有乱码

使用网页打开后发现是一个输入框

我们把最后的eval()函数换成console.log()过滤一下乱码

再重新排版一下得到：

function $(){
    var e=document.getElementById("c").value;
    if(e.length==16)//输入参数要为16位
        if(e.match(/^be0f23/)!=null) //
            if(e.match(/233ac/)!=null)
                if(e.match(/e98aa$/)!=null)
                    if(e.match(/c7be9/)!=null){
                        var t=["fl","s_a","i","e}"];
                        var n=["a","_h0l","n"];
                        var r=["g{","e","_0"];
                        var i=["it'","_","n"];
                        var s=[t,n,r,i];
                        for(var o=0;o<13;++o){
                            document.write(s[o%4][0]);s[o%4].splice(0,1)}
                        }
                    }
                    document.write('<input id="c"><button onclick=$()>Ok</button>');
delete _

审计代码后发现flag没有我们输入的参数，直接控制台运行：

    var t=["fl","s_a","i","e}"];
    var n=["a","_h0l","n"];
    var r=["g{","e","_0"];
    var i=["it'","_","n"];
    var s=[t,n,r,i];
    var r="";
    for(var o=0;o<13;++o){
        r+=s[o%4][0];
        s[o%4].splice(0,1);
    }
    r

得到flag