CVE-2020-8231: wrong connect-only connection
An application that performs multiple requests with libcurl's multi API
and sets the CURLOPT_CONNECT_ONLY option, might in rare circumstances
experience that when subsequently using the setup connect-only transfer,
libcurl will pick and use the wrong connection - and instead pick
another one the application has created since then.
CURLOPT_CONNECT_ONLY is the option to tell libcurl to not perform an
actual transfer, only connect. When that operation is completed, libcurl
remembers which connection it used for that transfer and "easy handle".
It remembers the connection using a pointer to the internal connectdata
struct in memory.
If more transfers are then done with the same multi handle before the
connect-only connection is used, leading to the initial connect-only
connection to get closed (for example due to idle time-out) while also
new transfers (and connections) are setup, such a new connection might
end up getting the exact same memory address as the now closed
If after those operations, the application then wants to use the
original transfer's connect-only setup to for example use
curl_easy_send() to send raw data over that connection, libcurl could
erroneously find an existing connection still being alive at the address
it remembered since before even though this is now a new and different
The application could then accidentally send data over that connection
which wasn't at all intended for that recipient, entirely unknowingly.