The update of proftpd-dfsg released as DLA-2338-1 incorrectly destroyed the memory pool in function sftp_kex_handle in contrib/mod_sftp/kex.c which may cause a segmentation fault and thus prevent sftp connections.

For Debian 9 stretch, this problem has been fixed in version 1.3.5e+r1.3.5b-4+deb9u2.

We recommend that you upgrade your proftpd-dfsg packages.

For the detailed security status of proftpd-dfsg please refer to its security tracker page at: https://security-tracker.debian.org/tracker/proftpd-dfsg

Further information about Debian LTS security advisories, how to apply these updates to your system and frequently asked questions can be found at: https://wiki.debian.org/LTS