Seroval: Deserialization invokes attacker-chosen callables: AsyncIteratorFactoryInstance calls source.on(listener) without type check

Summary

When fromJSON rebuilt an async iterator, it called on() on the iterator's source without checking that the source was a seroval stream. A crafted payload could pick another value as the source, such as a function returned by an application plugin. The deserializer then called that value's on method.

This is a variant of GHSA-mv8w-475r-vwqw. That fix covered the promise and stream control nodes but not the async iterator node.

Impact

An application that passes untrusted input to fromJSON with plugins that return callable values can have those callables invoked during deserialization. What this allows depends on what the plugin's values do.

Affected versions

• Versions up to 1.6.3 accept any value as the source.
• 1.6.4 rejects the reported payload.
• 1.6.5 to 1.6.7 check the source by node type, which a payload can get around by reusing a node id.
• All versions up to 1.6.7 should be treated as affected.

Patches

Fixed in seroval@1.6.8. Streams and sequences are now internal class instances. The deserializer checks the source value with instanceof, so plain data and plugin values are rejected no matter which node id they use.

Workarounds

Avoid plugins whose deserialize returns functions or objects with an on method when decoding untrusted input. Upgrading to 1.6.8 is recommended.