AIKIDO-2026-334136

TL;DR

ReadableStreamPlugin.deserialize in seroval-plugins casts the value read from the reference table to a Stream without a brand check and passes it to READABLE_STREAM_FACTORY_CONSTRUCTOR, whose start() callback runs synchronously during fromJSON and calls stream.on({...}) on that value. A crafted Reference node that points at an application object with an on method makes that method run during deserialization, before any error is raised. This is the same timing and type confusion primitive as the Promise resolver advisory GHSA-mv8w-475r-vwqw, reached through the ReadableStream plugin instead. The fix validates the backing source before it reaches the stream factory.