PHP反混淆实战 | 手把手带你入门PHP-Parser
1 什么是PHP-Parser ? PHP-Parser是由Nikic开发的一款PHP抽象语法树（AST）解析工具。能够将PHP代码转换为抽象语法树，安全研究员可以通过生成的语法树 2023-3-8 17:31:36 Author: 微步在线研究响应中心(查看原文) 阅读量:19 收藏
1 什么是PHP-Parser ? PHP-Parser是由Nikic开发的一款PHP抽象语法树（AST）解析工具。能够将PHP代码转换为抽象语法树，安全研究员可以通过生成的语法树 2023-3-8 17:31:36 Author: 微步在线研究响应中心(查看原文) 阅读量:19 收藏
什么是PHP-Parser ?
PHP-Parser入门
use PhpParser\ParserFactory;$parser = (new ParserFactory)->create(ParserFactory::PREFER_PHP7);
通过解析器的parse方法将PHP代码解析成抽象语法树：
<?phpuse PhpParser\Error;use PhpParser\ParserFactory;require 'vendor/autoload.php';$code = file_get_contents("./test.php");$parser = (new ParserFactory)->create(ParserFactory::PREFER_PHP7);try {$ast = $parser->parse($code);} catch (Error $error) {echo "Parse error: {$error->getMessage()}\n";}
//view.php<?phprequire 'vendor/autoload.php';use PhpParser\Error;use PhpParser\NodeDumper;use PhpParser\ParserFactory;//获取sample.php的代码内容$code = file_get_contents('sample.php');//初始化解析器$parser = (new ParserFactory)->create(ParserFactory::PREFER_PHP7);try {//解析sample.php内容，转换为ast$ast = $parser->parse($code);} catch (Error $error) {echo "Parse error: {$error->getMessage()}\n";return;}$dumper = new NodeDumper;//优化ast并dumpecho $dumper->dump($ast) . "\n";
<?php$a = 'a'.'ssert';$a($_POST['x']);=======array(0: Stmt_Expression(expr: Expr_Assign(var: Expr_Variable(name: a)expr: Expr_BinaryOp_Concat(left: Scalar_String(value: a)right: Scalar_String(value: ssert))))1: Stmt_Expression(expr: Expr_FuncCall(name: Expr_Variable(name: a)args: array(0: Arg(name: nullvalue: Expr_ArrayDimFetch(var: Expr_Variable(name: _POST)dim: Scalar_String(value: x))byRef: falseunpack: false))))
$prettyPrinter = new PrettyPrinter\Standard;$prettyCode = $prettyPrinter->prettyPrintFile($ast);echo $prettyCode;
“PhpParser\NodeVisitor“接口，该接口定义4个遍历方法：
//方法在遍历开始之前调用public function beforeTraverse(array $nodes);//在遍历子节点之前调用public function enterNode(\PhpParser\Node $node);//在离开当前节点时调用public function leaveNode(\PhpParser\Node $node);//在遍历之后调用一次public function afterTraverse(array $nodes)
PHP-Parser实战
1.字符二元操作符还原
针对字符串的异或、拼接、与或非等操作进行还原，基础样本如下：
<?php$a = 'a'.'s'.'s'.'e'.'r'.'t';$a($_POST['x']);?>
首先输出AST进行查看。
array(0: Stmt_Expression(expr: Expr_Assign(var: Expr_Variable(name: a)expr: Expr_BinaryOp_Concat(left: Expr_BinaryOp_Concat(left: Expr_BinaryOp_Concat(left: Expr_BinaryOp_Concat(left: Expr_BinaryOp_Concat(left: Scalar_String(value: a)right: Scalar_String(value: s))right: Scalar_String(value: s))right: Scalar_String(value: e))right: Scalar_String(value: r))right: Scalar_String(value: t))))1: Stmt_Expression(expr: Expr_FuncCall(name: Expr_Variable(name: a)args: array(0: Arg(name: nullvalue: Expr_ArrayDimFetch(var: Expr_Variable(name: _POST)dim: Scalar_String(value: x))byRef: falseunpack: false)))))
class BinaryOpReducer extends NodeVisitorAbstract{public function leaveNode(Node $node) {if ($node instanceof Node\Expr\BinaryOp\Concat && $node->left instanceof Node\Scalar\String_ && $node->right instanceof Node\Scalar\String_) {return new PhpParser\Node\Scalar\String_($node->left->value . $node->right->value);}}}
<?php$a = 'assert';$a($_POST['x']);
判断当前节点是否为”Scalar\String_”； 将节点的”value”值进行“base64_encode“编码； 替换原节点为“FuncCall“类型；
class Base64Reducer extends NodeVisitorAbstractpublic function leaveNode(Node $node) {if ($node instanceof Node\Scalar\String_) {$name = $node->value;return new Expr\FuncCall(new Node\Name("base64_decode"),[new Node\Arg(new Node\Scalar\String_(base64_encode($name)))]);}}}
<?php$str = "Threatbook";?>--After parser:--$str = base64_decode('VGhyZWF0Ym9vaw==');
筛选所有“Variable“类型的节点； 通过正则表达式匹配出乱码变量，这种变量名中不会出现字母数字等字符； 通过一个数组存放重命名的变量名，如果某个乱码变量再次出现，通过数组查询新的变量名进行替换。
代码如下：
// 变量重命名class ReNameVariable extends NodeVisitorAbstract{public $Count = 0;public $NewName = [];public function leaveNode(Node $node){//判断Variable类型的节点if ($node instanceof Node\Expr\Variable) {//匹配不含字母数字的乱码变量if (!preg_match('/^[a-zA-Z0-9_]+$/', $node->name)) {//如果这个变量再次出现，使用已经有的替换值进行替换if (in_array($node->name, array_keys($this->NewName))){$new_var_name = str_replace($node->name, 'v_' . $this->NewName[$node->name], $node->name);return (new Node\Expr\Variable($new_var_name));}else{//记录新的变量名到数组$this->NewName[$node->name] = $this->Count++;$new_var_name = str_replace($node->name, 'v_' . $this->NewName[$node->name], $node->name);return (new Node\Expr\Variable($new_var_name));}}return ;}}
可以看到原本的不可见变量名已经被重命名成了“v_“格式的变量。同时可以观察到“GLOBALS“变量的键名也是乱码字符，借鉴变量名重命名的思路对所有”GLOBALS“数组的键名进行重命名：
筛选所有的“ArrayDimFetch“类型节点,且代码样式为”$GLOBALS[XX][X]“,对”$node->var“和”$node->dim“也进行判断； 通过正则表达式匹配出乱码数组键名，这种键名中不会出现字母数字等字符； 通过一个数组存放重命名的键名名，如果某个乱码键名再次出现，通过数组查询新的变量名进行替换。
和上面不同的是我们恢复的是二维数组，所以要多包含一层判断：
class ReNameArrayKeyValue extends NodeVisitorAbstract{private $Count = [];private $NewName = [];public function leaveNode(Node $node){if ( $node instanceof Node\Expr\ArrayDimFetch && !($node->var instanceof Node\Expr\ArrayDimFetch) && !($node->dim instanceof Node\Expr\ArrayDimFetch) ) {$key = $node->dim->value;$name = $node->var->name;if (!preg_match('/^[a-zA-Z0-9_]+$/', $key)) {if ($this->Count[$name] !== null){// 判断该数组当前键值if ($this->NewName[$name][$key] !== null){$new_key_name = str_replace($key, 'arr_' . $this->NewName[$name][$key], $key);return new Node\Expr\ArrayDimFetch( new Node\Expr\Variable($name), new Node\Scalar\String_($new_key_name) );}else{// 未替换该键值的操作$this->NewName[$name][$key] = $this->Count[$name]++;$new_key_name = str_replace($key, 'arr_' . $this->NewName[$name][$key], $key);return new Node\Expr\ArrayDimFetch( new Node\Expr\Variable($name), new Node\Scalar\String_($new_key_name) );}}else{$this->NewName[$name] = [];$this->Count[$name] = 0;$this->NewName[$name][$key] = $this->Count[$name]++;$new_key_name = str_replace($key, 'arr_' . $this->NewName[$name][$key], $key);return new Node\Expr\ArrayDimFetch( new Node\Expr\Variable($name), new Node\Scalar\String_($new_key_name) );}}return ;}}}
筛选“FuncCall”节点，判断节点的”$node->expr->name->parts[0]”是否为”unserialize”,节点”$node->expr->args[0]->value->name->parts[0]”的值是否为”base64_decode”； 筛选”FuncCall”节点，判断节点的”$node->expr->name->value”是否为”unserialize”,节点”$node->expr->args[0]->value->name->value”的值是否为”base64_decode”,这种判断是因为上图中的第二次还原的调用形式为”('unserialize')(('base64_decode')('xxx')”,PHP支持字符串调用的方式，在AST中会解析为”String_”节点； 获取加密的值，直接返回”unserialize(base64_decode(密文))”的值； 同时还原数组是需要判断”GLOBALS”的值是否存在。
class ArrayToConstant extends NodeVisitorAbstract{public $variableName = '';public $constants = [];public function enterNode(Node $node)//unserialize(base64_decode(类型的调用if ($node instanceof Node\Expr\Assign &&$node->expr instanceof Node\Expr\FuncCall &&$node->expr->name instanceof Node\Name &&is_string($node->expr->name->parts[0]) &&$node->expr->name->parts[0] == 'unserialize' &&count($node->expr->args) === 1 &&$node->expr->args[0] instanceof Node\Arg &&$node->expr->args[0]->value instanceof Node\Expr\FuncCall &&$node->expr->args[0]->value->name instanceof Node\Name &&is_string($node->expr->args[0]->value->name->parts[0]) &&$node->expr->args[0]->value->name->parts[0] == 'base64_decode') {$string = $node->expr->args[0]->value->args[0]->value->value;$array = unserialize(base64_decode($string));$this->variableName = $node->var->name;$this->constants = $array;return new Node\Expr\Assign($node->var, Node\Scalar\LNumber::fromString("0"));}else if(//('unserialize')(('base64_decode')类型的调用$node instanceof Node\Expr\Assign &&$node->expr instanceof Node\Expr\FuncCall &&$node->expr->name instanceof Node\Scalar\String_ &&is_string($node->expr->name->value) &&$node->expr->name->value == 'unserialize' &&count($node->expr->args) === 1 &&$node->expr->args[0] instanceof Node\Arg &&$node->expr->args[0]->value instanceof Node\Expr\FuncCall &&$node->expr->args[0]->value->name instanceof Node\Scalar\String_ &&is_string($node->expr->args[0]->value->name->value) &&$node->expr->args[0]->value->name->value == 'base64_decode'){$string = $node->expr->args[0]->value->args[0]->value->value;$array = unserialize(base64_decode($string));$this->variableName = $node->var->name;$this->constants = $array;return new Node\Expr\Assign($node->var, Node\Scalar\LNumber::fromString("0"));}else{return;}}public function leaveNode(Node $node)if ($this->_variableName === '') return;if ($node instanceof Node\Expr\ArrayDimFetch && $node->var->name === $this->_variableName) {$val = $this->constants[$node->dim->value];//判断该 GLOBALS 值是否存在if ($val === null){return;}if (is_string($val)) {return new Node\Scalar\String_($val);} elseif (is_double($val)) {return new Node\Scalar\DNumber($val);} elseif (is_int($val)) {return new Node\Scalar\LNumber($val);} else {return new Node\Expr\ConstFetch(new Node\Name\FullyQualified(json_encode($val)));}}}}
class ExpressionToNumber extends NodeVisitorAbstractpublic function leaveNode(Node $node){if ($node instanceof Node\Expr\BinaryOp\Plus &&($node->left instanceof Node\Scalar\LNumber || $node->left instanceof Node\Scalar\String_ || $node->left instanceof Node\Expr\UnaryMinus) && $node->right instanceof Node\Expr\BinaryOp\Minus && ($node->right->left instanceof Node\Scalar\LNumber || $node->right->left instanceof Node\Scalar\String_) && ($node->right->right instanceof Node\Scalar\LNumber || $node->right->right instanceof Node\Scalar\String_)) {if ($node->left instanceof Node\Expr\UnaryMinus) {$a = -($node->left->expr->value);} else {$a = $node->left->value;}$b = $node->right->left->value;$c = $node->right->right->value;return new Node\Scalar\LNumber($a + $b - $c);}}}
class ChrReducer extends NodeVisitorAbstract {public function leaveNode(Node $node){if ($node instanceof Node\Expr\FuncCall && is_string($node->name->value) && $node->name->value == 'chr' && count($node->args) === 1 && $node->args[0] instanceof Node\Arg && $node->args[0]->value instanceof Node\Scalar\LNumber){$char = $node->args[0]->value->value;return new Node\Scalar\String_(chr($char));}}}class ConcatReducer extends NodeVisitorAbstract{public function leaveNode(Node $node)if ($node instanceof Node\Expr\BinaryOp\Concat){if ($node->left instanceof Node\Scalar\String_ && is_string($node->left->value) && $node->right instanceof Node\Scalar\String_ && is_string($node->right->value)){return new Node\Scalar\String_($node->left->value . $node->right->value);}}}}class Rot13Reducer extends NodeVisitorAbstract{public function leaveNode(Node $node){if ($node instanceof Node\Expr\FuncCall && $node->name instanceof Node\Scalar\String_ &&is_string( $node->name->value ) &&$node->name->value == 'str_rot13' &&count( $node->args ) === 1 &&$node->args[0] instanceof Node\Arg &&$node->args[0]->value instanceof Node\Scalar\String_ &&is_string($node->args[0]->value->value)){return new Node\Scalar\String_(str_rot13($node->args[0]->value->value));}}}
结语
参考链接
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