The code in src/sftpserver.c did not verify the validity of certain pointers and expected them to be valid. A NULL pointer dereference could have been occurred that typically causes a crash and thus a denial-of-service.

For Debian 9 stretch, this problem has been fixed in version 0.7.3-2+deb9u3.

We recommend that you upgrade your libssh packages.

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

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