Hono: Unbounded dot-notation nesting in `parseBody()` can cause memory exhaustion

NVD Description

### Summary When `parseBody()` expands dot-separated form field names into nested objects, it does not limit the nesting depth or the total number of objects created. A request body well within a normal size limit can therefore allocate an object graph far larger than the request itself, and concurrent requests can exhaust the heap and terminate the process. ### Details Each dot-separated segment of a field name creates an intermediate object. Neither the segments within a single field name nor the total across a request was bounded, and empty segments were preserved, so a field name could encode one nesting level per byte. Both shapes produce the effect: a single deeply dotted field name, and a large number of shallowly dotted ones within one body. A request body size limit does not prevent it, because the amplification happens after the body has been accepted. Dot-notation parsing is not enabled by default. ### Impact An attacker who can reach an endpoint that parses request bodies with dot-notation enabled can send concurrent requests whose memory cost is disproportionate to their size. This may lead to: - exhaustion of the JavaScript heap and termination of the server process - the service remaining unavailable until it is restarted This issue affects applications that explicitly enable dot-notation parsing. Applications using the default behaviour are not affected.

Affected Packages (1)