CURL-CVE-2018-1000005

HTTP/2 trailer out-of-bounds read

libcurl contains an out bounds read in code handling HTTP/2 trailers. It was [reported](https://github.com/curl/curl/pull/2231) that reading an HTTP/2 trailer could mess up future trailers since the stored size was one byte less than required. The problem is that the code that creates HTTP/1-like headers from the HTTP/2 trailer data once appended a string like `":"` to the target buffer, while this was recently changed to `": "` (a space was added after the colon) but the associated math was not updated correspondingly. When accessed, the data is read out of bounds and causes either a crash or that the (too large) data gets passed to the libcurl callback. This might lead to a denial-of-service situation or an information disclosure if someone has a service that echoes back or uses the trailers for something.