Arai-A

**Name of the Vulnerable Software and Affected Versions** ECMAScript (affected versions not specified) **Description** A problem in the ECMAScript specification of async generators may lead to mis-implementation in a way that could present as a security issue, such as type confusion and pointer dereference. The internal async generator machinery calls regular promise resolver functions on IteratorResult objects, assuming that these objects will not be then-ables. However, these objects can be made then-able, triggering arbitrary behavior, including re-entering the async generator machinery in a way that violates some internal invariants. **Recommendations** At the moment, there is no information about a newer version that contains a fix for this vulnerability. Implementors should refer to the latest ECMAScript specification and update their implementations to comply with the `AsyncGenerator` section. Users unable to upgrade to the patched version would want to use exception handling mechanisms to ensure any exceptions caused by the engine don't impact the availability of the main application.

**Name of the Vulnerable Software and Affected Versions** Boa versions 0.16 through 0.19.0 **Description** A wrong assumption in Boa's implementation of `AsyncGenerator` can cause an uncaught exception on certain scripts. This occurs because the state of an `AsyncGenerator` object is assumed not to change while resolving a promise created by methods such as `%AsyncGeneratorPrototype%.next`, `%AsyncGeneratorPrototype%.return`, or `%AsyncGeneratorPrototype%.throw`. However, a carefully constructed code can trigger a state transition from a getter method for the promise's `then` property, causing the engine to fail an assertion of this assumption and resulting in an uncaught exception. This could be used to create a Denial Of Service attack in applications that run arbitrary ECMAScript code provided by an external user. **Recommendations** For versions 0.16 through 0.19.0, upgrade to version 0.19.0 to correctly handle this case. For users unable to upgrade to the patched version, use `std::panic::catch unwind` to ensure any exceptions caused by the engine do not impact the availability of the main application.