In QUIC in RFC 9000, the Latency Spin Bit specification (section 17.4) does not strictly constrain the bit value when the feature is disabled, which might allow remote attackers to construct a covert channel with data represented as changes to the bit value. NOTE: The "Sheridan, S., Keane, A. (2015). In Proceedings of the 14th European Conference on Cyber Warfare and Security (ECCWS), University of Hertfordshire, Hatfield, UK." paper says "Modern Internet communication protocols provide an almost infinite number of ways in which data can be hidden or embed whithin seemingly normal network traffic."
The web application does not, or cannot, sufficiently verify whether a request was intentionally provided by the user who sent the request, which could have originated from an unauthorized actor.