A detailed example of the security problem of PHP comparison operators _php

Source: Internet
Author: User

PHP comparison operators have = = (equals) loose comparison, = = = (exactly equal to) strict comparison, where the face will introduce a lot of interesting questions.

When loosely compared, PHP will unify their type, such as character to number, non-bool type to bool type, in order to avoid unexpected running effect, should use strict comparison. The following is a table of comparison operators on PHP manual:

The example name results $ A = = $b equals TRUE if $a equals $b after the type conversion. $a = = = $b congruent TRUE if $a equals $b, and they are of the same type. $a! = $b unequal to TRUE if the type is converted $a not equal to $b. $a <> $b Not equal to TRUE if the type is converted $a does not equate to $b. $a!== $b Not equal to TRUE if $a are not equivalent to $b, or they are of different types. $a < $b small with TRUE if the $a is strictly less than $b. $a > $b is greater than TRUE if the $a is strictly greater than $b. $a <= $b is less than or equal to TRUE if $a is less than or equal to $b. $a >= $b is greater than or equal to TRUE if $a is greater than or equal to $b.

0X01 Security Issues

1 Hash comparison defects

PHP in the processing of hash string will use!=,== to hash comparison, if the hash value starts with 0e, behind is the number, and then compared with the number, will be interpreted as 0*10^n or 0, will be judged equal, bypassing the login link.

root@kali:~/tool# php-r ' Var_dump ("00e0345" = = "0"), Var_dump ("0e123456789" = = "0"), Var_dump ("0e1234abc" = = "0"); '
BOOL (TRUE)
BOOL (TRUE)
BOOL (FALSE)

When all is the number, the loose comparison will perform the best effort mode, such as 0e12345678 will be interpreted as 0*10^12345678, except that the E is not all the number is not equal, this can be seen from Var_dump ("0e1234abc" = = "0").

2 BOOL Spoofing

When Json_decode and unserialize are present, some structures are interpreted as bool types, which can also cause deception. Json_decode Sample code:

$json _str = ' {' user ': true, ' Pass ': true} '; $data = Json_decode ($json _str,true); if ($data [' user '] = = ' Admin ' && $ data[' Pass ']== ' secirity ') {  print_r (' logined in as bool '). \ n ");}

Operation Result:

root@kali:/var/www# php/root/php/hash.php
Logined in as bool

Unserialize Sample code:

$unserialize _str = ' a:2:{s:4: "User", B:1;s:4: "Pass"; b:1;} '; $data _unserialize = unserialize ($unserialize _str), if ($data _unserialize[' user '] = = ' Admin ' && $data _ unserialize[' Pass ']== ' secirity ') {  print_r (' logined in Unserialize '. ") \ n ");}

The results of the operation are as follows:

root@kali:/var/www# php/root/php/hash.php
Logined in Unserialize

3 Number Conversion Spoofing

$user _id = ($_post[' user_id ')), if ($user _id = = "1") {  $user _id = (int) ($user _id);  # $user _id = intval ($user _id);  $qry = "SELECT * from ' users ' WHERE user_id= ' $user _id ';";} $result = mysql_query ($qry) or Die ('
' . Mysql_error (). '
');p Rint_r (Mysql_fetch_row ($result));

Send user_id=0.999999999999999999999 to get the result as follows:

Array
(
[0] = 0
[1] = LXX '
[2] = =
[3] = =
[4] = =
[5] = =
)

Originally is to query user_id data, the result is user_id=0 data. int and intval are low when converting numbers, and then the following code:

if ($_post[' uid ']! = 1) {$res = $db->query ("SELECT * from user WHERE uid=%d", (int) $_post[' uid ']); mail (...);} else { Die ("Cannot reset password of admin");}

If you pass in 1.1, you bypass the $_post[' UID '! =1 's judgment, you can operate on the uid=1 user. In addition, Intval also has an effort mode, that is, to convert all the numbers until it encounters a non-digit, if using:

if (intval ($qq) = = = ' 123456 ') {  $db->query ("select * from user where QQ = $QQ")}

An attacker enters 123456 Union select version () to attack.

4 PHP5.4.4 Special Cases

A modification of this version of PHP resulted in an overflow of two numeric characters resulting in a comparison of equal

$ Php-r ' var_dump ("61529519452809720693702583126814" = = "61529519452809720000000000000000"); '
BOOL (TRUE)

3 Off-topic:

There are similar problems with the PHP strcmp function, which is explained on manual, int strcmp (string $str 1, String $str 2), STR1 is the first string, STR2 is the second string, if str1 is less than str2, returns <0, if STR1>STR2, return >0, both return equal to 0, if STR2 is an array?

$_get[' key ' = Array (); $key = "Llocdpocuzion5dcp2bindhspiccy"; $flag = strcmp ($key, $_get[' key ']); if ($flag = = 0) {  PR int "welcome!";} else {  print "bad key!";}

Operation Result:

root@kali:~/php# PHP strcmp.php
PHP warning:strcmp () expects parameter 2 to is string, array given in/root/php/strcmp.php on line 13
welcome!

Compare multiple types

Number of operations 1 types Number of operations 1 types result
null or string string will NULL to "" for numeric or lexical comparisons
bool or null Any other type Converted to BOOL,FALSE < TRUE
Object Object Built-in classes can define their own comparisons, non-homogeneous cannot be compared, the same class and arrays are the same way to compare properties (PHP 4), PHP 5 has its own description
string , resource or number string , resource or number Converts strings and resources to numbers, compared by ordinary mathematics
Array Array Arrays with fewer members are smaller if the keys in the operand 1 do not exist in the operand 2, the array cannot be compared, otherwise the values are compared (see example below)
Array Any other type Array always bigger.
Object Any other type Object always bigger.
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