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EXTERNAL: OSError: [Errno 48] Address already in use


Dan Stromberg <drsalists at gmail.com>:
> [on how SO_REUSEADDR is a security risk]

> Start an echo server process P that listens on tcp/5555.
>
> Initiate a connection from a client machine to process P at tcp/5555. It
> works as expected.
>
> Kill P.
>
> Initiate a connection from a client machine to process P at tcp/5555.  It
> gives a connection refused as expected.
>
> If someone else comes along soon after and starts a different echo server
> process Q at tcp/5555 on the same server, it starts up immediately if P
> used SO_REUSEADDR.
>
> Then initiate a connection from the same (or different) client machine to
> process P (which no longer exists).  Q gets the data intended for P.

Well, the same security issue can be demonstrated without SO_REUSEADDR:

   DON'T start an echo server process P that listens on tcp/5555.

   Initiate a connection from a client machine to process P at tcp/5555.  It
   gives a connection refused as expected.

   If someone else comes along and starts an echo server process Q at
   tcp/5555 on the same server, it starts up immediately.

   Then initiate a connection from the same (or different) client machine to
   process P (which never existed).  Q gets the data intended for P.


The security issue can be real but is not directly related with
SO_REUSEADDR.


Marko