Affected: Homebrew: livereload

## Summary

`HTTPServerRequest.__init__` in `tornado/httputil.py` parses the URL query string via `parse_qs_bytes()` with no field-count limit — while the sibling POST-body parsing path (`parse_body_arguments`) received a `max_num_fields=1000` cap added earlier in this exact same release (v6.5.8, commit `8d6363ed`), explicitly to bound parsing cost for the identical underlying primitive. This leaves the query-string path with the resource-exhaustion exposure the body-path fix was meant to close.

**File**: `tornado/httputil.py`, line 553 (`HTTPServerRequest.__init__`)

### Root Cause

```python # tornado/httputil.py:553 (before fix) self.arguments = parse_qs_bytes(self.query, keep_blank_values=True) ```

Compare with the POST-body path fixed one commit earlier in the same release:

```python # tornado/httputil.py:1038-1041 uri_arguments = parse_qs_bytes( body, keep_blank_values=True, max_num_fields=config.urlencoded.max_arguments, # default 1000 ) ```

Both call sites funnel through the same `tornado.escape.parse_qs_bytes` (a thin wrapper over `urllib.parse.parse_qs`), which is exactly why `max_num_fields` was added to `urllib.parse.parse_qsl` upstream — to let frameworks bound field count. The fix was applied only to the body path; the query-string path was missed.

The request line + headers together are capped at `max_header_size` (default 65536 bytes), so this is not literally unbounded, but a single ~64KB request line can carry thousands of short `key=value…

Tornado before 6.5.9 fails to limit the number of query string fields in HTTPServerRequest.__init__, allowing remote attackers to cause event-loop stalling by sending requests with thousands of query parameters. Attackers can send unauthenticated GET requests with unbounded query-string field counts to degrade response times for all clients sharing the same IOLoop.

Tornado before 6.5.9 fails to limit the number of query string fields in HTTPServerRequest.__init__, allowing remote attackers to cause event-loop stalling by sending requests with thousands of query parameters. Attackers can send unauthenticated GET requests with unbounded query-string field counts to degrade response times for all clients sharing the same IOLoop.

Affected: Ubuntu:Pro:16.04:LTS: python-tornado, Ubuntu:Pro:18.04:LTS: python-tornado, Ubuntu:Pro:20.04:LTS: python-tornado, Ubuntu:Pro:22.04:LTS: python-tornado, Ubuntu:24.04:LTS: python-tornado, Ubuntu:26.04:LTS: python-tornado

Tornado before 6.5.9 fails to limit the number of query string fields in HTTPServerRequest.__init__, allowing remote attackers to cause event-loop stalling by sending requests with thousands of query parameters. Attackers can send unauthenticated GET requests with unbounded query-string field counts to degrade response times for all clients sharing the same IOLoop.