The server in Dropbear before 2017.75 might allow post-authentication root remote code execution because of a double free in cleanup of TCP listeners when the -a option is enabled.
https://security.netapp.com/advisory/ntap-20191004-0006/
http://www.debian.org/security/2017/dsa-3859
http://lists.ucc.gu.uwa.edu.au/pipermail/dropbear/2017q2/001985.html