CVE-2025-52570

Letmein is an authenticating port knocker. Prior to version 10.2.1, The connection limiter is implemented incorrectly. It allows an arbitrary amount of simultaneously incoming connections (TCP, UDP and Unix socket) for the services letmeind and letmeinfwd. Therefore, the command line option num-connections is not effective and does not limit the number of simultaneously incoming connections. This issue has been patched in version 10.2.1.

Letmein is an authenticating port knocker. Prior to version 10.2.1, The connection limiter is implemented incorrectly. It allows an arbitrary amount of simultaneously incoming connections (TCP, UDP and Unix socket) for the services letmeind and letmeinfwd. Therefore, the command line option num-connections is not effective and does not limit the number of simultaneously incoming connections. This issue has been patched in version 10.2.1.

### Impact The connection limiter is implemented incorrectly. It allows an arbitrary amount of simultaneously incoming connections (TCP, UDP and Unix socket) for the services `letmeind` and `letmeinfwd`. Therefore, the command line option `num-connections` is not effective and does not limit the number of simultaneously incoming connections. `letmeind` is the public network facing daemon (TCP/UDP). `letmeinfwd` is the internal firewall daemon that only listens on local Unix socket. Possible Denial Of Service by resource exhaustion. ### Affected versions All versions `<= 10.2.0` are affected. ### Patches All users shall upgrade to version `10.2.1`. ### Workarounds Untested possible workarounds: - It might be possible to limit the number of active connections to the `letmeind` port (default 5800) via firewall. - The resource consumption of the service might be restricted with a service manager such as systemd. ### Severity: If a (D)DoS is run against the service, *something* is going to be affected. The connection limiter assures that the effect on the system itself is limited at the expense of the effect on the letmein services itself. So even with the connection limiter active, a (D)DoS can lead to a less responsive or unresponsive letmein service.

### Impact The connection limiter is implemented incorrectly. It allows an arbitrary amount of simultaneously incoming connections (TCP, UDP and Unix socket) for the services `letmeind` and `letmeinfwd`. Therefore, the command line option `num-connections` is not effective and does not limit the number of simultaneously incoming connections. `letmeind` is the public network facing daemon (TCP/UDP). `letmeinfwd` is the internal firewall daemon that only listens on local Unix socket. Possible Denial Of Service by resource exhaustion. ### Affected versions All versions `<= 10.2.0` are affected. ### Patches All users shall upgrade to version `10.2.1`. ### Workarounds Untested possible workarounds: - It might be possible to limit the number of active connections to the `letmeind` port (default 5800) via firewall. - The resource consumption of the service might be restricted with a service manager such as systemd. ### Severity: If a (D)DoS is run against the service, *something* is going to be affected. The connection limiter assures that the effect on the system itself is limited at the expense of the effect on the letmein services itself. So even with the connection limiter active, a (D)DoS can lead to a less responsive or unresponsive letmein service.

Letmein es un bloqueador de puertos de autenticación. Antes de la versión 10.2.1, el limitador de conexiones estaba implementado incorrectamente. Permitía un número arbitrario de conexiones entrantes simultáneas (TCP, UDP y socket Unix) para los servicios letmeind y letmeinfwd. Por lo tanto, la opción de línea de comandos num-connections no es efectiva y no limita el número de conexiones entrantes simultáneas. Este problema se ha corregido en la versión 10.2.1.