MCP PHP SDK: client HttpTransport SSE buffer (sseBuffer .= chunk) grows unbounded when server withholds the event delimiter

Summary The HTTP client transport in mcp/sdk reads a Server-Sent-Events SSE response stream incrementally and appends each 4 KiB chunk to an in-memory buffer $this-sseBuffer .= $chunk; with no upper bound. The buffer is only ever flushed when an SSE event delimiter "\n\n" appears. A remote MCP...

PT-2026-80244

Summary The HTTP client transport in mcp/sdk reads a Server-Sent-Events SSE response stream incrementally and appends each 4 KiB chunk to an in-memory buffer $this-sseBuffer .= $chunk; with no upper bound. The buffer is only ever flushed when an SSE event delimiter " " appears. A remote MCP serve...