react/http is an event-driven, streaming HTTP client and server implementation for ReactPHP. From 1.0.0 until 1.11.1, React\Http\Browser uses ClientRequestStream::handleData() to append response-header bytes to an internal buffer without enforcing a size limit. A remote server can send a valid status line and partial header, withhold the \r\n\r\n or \n\n header terminator, and continue streaming data so the buffer grows for the life of the connection. Applications that fetch attacker-controlled or attacker-influenced URLs, including URLs reached through redirects, can exhaust PHP memory_limit and crash the event-loop or worker process. Confidentiality and integrity are unaffected. This issue is fixed in version 1.11.1.

Affected: Packagist: react/http

### Summary

`React\Http\Browser` and its lower-level HTTP stack impose no limit on the size of a response's header section while it is being received. `ClientRequestStream::handleData()` appends every incoming byte to an internal buffer and only scans that buffer for the `\r\n\r\n` (or `\n\n`) terminator, without ever checking its length. A remote server that withholds the terminator and keeps streaming can grow the client's memory without bound until PHP's `memory_limit` is exhausted and the process crashes.

This is an unauthenticated, network-reachable denial of service against any application that uses `react/http` as a client to fetch untrusted or attacker-influenced URLs, including via redirects.

### Details

`ClientRequestStream::handleData()` is bound directly to the underlying connection's `data` event, so every byte the peer sends is appended with no size check:

```php public function handleData($data) { $this->buffer .= $data;

// buffer until double CRLF (or double LF for compatibility with legacy servers) $eom = \strpos($this->buffer, "\r\n\r\n"); $eomLegacy = \strpos($this->buffer, "\n\n"); if ($eom !== false || $eomLegacy !== false) { ```

The only exit from the buffering state is finding the header terminator or a connection close, so until it arrives the buffer grows monotonically for as long as the peer keeps sending.

The codebase already applies this class of limit elsewhere, but not symmetrically. `RequestHeaderParser` caps incomin…