TL;DR What: Gammu SMSD — the daemon behind a huge number of SMS gateways, alerting rigs and 2FA senders — runs an operator-configured hook every time a text arrives. With the Files backend and RunOnReceive enabled, the SMS sender ID was escaped for use as a filename but not for the shell , and then appended to a /bin/sh -c command line. A sender ID containing shell metacharacters executed arbitrary commands as the gammu-smsd user. Impact: Remote, unauthenticated code...