An invalid memory access issue could be triggered remotely in the SFTP component of PSFTPd. This issue could be triggered prior authentication. The PSFTPd server did not automatically restart, which enabled attackers to perform a very effective DoS attack against this service. By sending the following SSH identification / version string to the server, a NULL pointer dereference could be triggered: $ cat tmp.14 SSH-2.0-BBBBBBBB CCCCCCCCCCCC $ cat tmp.14 | socat - TCP:192.168.122.50:22 The issue appears to be a race condition in the window message handling, performing the cleanup for invalid connections. Upon further investigation X41 D-Sec GmbH could confirm that the accessed memory was already freed.