Riverline/Multipart-Parser
The issue arises when Bref is used with the Event-Driven Function runtime and the handler is a `RequestHandlerInterface`. During the conversion of a Lambda event to a PSR7 object, if the request is a MultiPart, each part is parsed, and the `Content-Type` header of each part is read using the `Riverline/multipart-parser` library. This library performs slow multi-byte string operations on the header value, specifically using the `mb convert encoding` function with parameters read from the header value. An attacker could send crafted requests to force the server into long operations, resulting in a long billed duration. The attack requires the Lambda to use the Event-Driven Function runtime, implement at least an endpoint accepting POST requests, and the attacker can send requests up to 6MB long. If the Lambda uses a PHP runtime <= php-82, the impact is higher.