Vulnerability on Swift 5.1.x < 5.1.5

[mbarnach]

Context and Description

The Swift team disclose a security issue in Swift >=5.1 < 5.1.5 about the JSON serialization.
A Kitura app build with such version is vulnerable to a DDOS.
The Swift version 5.1.5 fixes it: https://forums.swift.org/t/swift-5-1-5-for-linux/34478

This is not a Kitura specific problem, but worth a mention I think, maybe in the README?

Environment Details

Swift 5.1x. < 5.1.5, Linux only

Steps to Reproduce

1. create an endpoint that accept a payload
2. send a payload with a lot of '['
3. compile on Linux with Swift 5.1 < 5.1.5
4. observe the crash