Memory Allocation with Excessive Size Value in github.com/gofiber/fiber

Summary

Fiber is an Express inspired web framework written in Go. In versions through 2.52.8 and 3.0.0-beta.2 through 3.0.0-beta.3, when using Fiber's `Ctx.BodyParser` to parse form data containing a large numeric key that represents a slice index (e.g., `test.18446744073704`), the application crashes due to an out-of-bounds slice allocation in the underlying schema decoder. The root cause is that the decoder attempts to allocate a slice of length `idx + 1` without validating whether the index is within a safe or reasonable range. If the `idx` is excessively large, this leads to an Integer Overflow or Memory Exhaustion, causing a panic or crash.