FTP PWD response parser out of bounds read
libcurl may read outside of a heap allocated buffer when doing FTP.
When libcurl connects to an FTP server and successfully logs in
(anonymous or not), it asks the server for the current directory with
the PWD command. The server then responds with a 257 response containing
the path, inside double quotes. The returned path name is then kept by
libcurl for subsequent uses.
Due to a flaw in the string parser for this directory name, a directory
name passed like this but without a closing double quote would lead to
libcurl not adding a trailing NUL byte to the buffer holding the name.
When libcurl would then later access the string, it could read beyond
the allocated heap buffer and crash or wrongly access data beyond the
buffer, thinking it was part of the path.
A malicious server could abuse this fact and effectively prevent
libcurl-based clients to work with it - the PWD command is always issued
on new FTP connections and the mistake has a high chance of causing a
segfault.