I have just tested in a Docker container on sid and with that version (libssh2-1 1.9.0-3) ECDSA works (makes sense when I look at the changelog). The memory leak is still there.
- Bug#959881: libssh2-1: Please upgrade to 1.9: ECDSA a... Benjamin Riefenstahl
- Bug#959881: libssh2-1: Please upgrade to 1.9: EC... Benjamin Riefenstahl