CURL-CVE-2018-1000005

libcurl contains an out bounds read in code handling HTTP/2 trailers.

It was reported 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.