libcurl versions from 7.34.0 to before 7.64.0 are vulnerable to a heap out-of-bounds read in the code handling the end-of-response for SMTP. If the buffer passed to "smtp_endofresp()" isn't NUL terminated and contains no character ending the parsed number, and "len" is set to 5, then the "strtol()" call reads beyond the allocated buffer. The read contents will not be returned to the caller.