If PAM is configured to read user-specified environment variables and UseLogin=yes in sshdconfig, then a hostile local user may attack /bin/login via LDPRELOAD or similar environment variables set via PAM.
Upstream fix:
https://anongit.mindrot.org/openssh.git/commit/?id=85bdcd7c92fe7ff133bbc4e10a65c91810f88755
Debian advisory:
https://www.debian.org/security/2016/dsa-3550