[radext] Re: Selfie Attack on TLS-PSK

[Alan DeKok <[e-mail]>]

On Jul 25, 2024, at 11:23 AM, Margaret Cullen <[e-mail]> wrote:
> As Stefan points out, copying of a RADIUS/TLS-transmitted RADIUS message on to a local network is different (and less secure) than dumb copying of a message that was transmitted via RADIUS/UDP, because sensitive data in the message transmitted via UDP will still be protected (to some degree) by the RADIUS secret and MD5, while the packet coming from RADIUS/TLS would use a well-known RADIUS secret, “radsec”, essentially equivalent to sending the sensitive parts of the packet in clear text.

  I think that description is not correct, though.  The RADIUS packets have some kind of transport behavior (TLS, shared secrets, whatever).  That behavior is defined hop by hop.  So when a proxy forwards traffic, it doesn't care what the previous transport is.

  i.e. When packets go from A->B, and then B->C, the transport profile for A->B has zero impact on the transport profile for B->C.

  The proxy "B" uses the following process:

1) receive packets from A using whatever transport is there

2) uses the "A" profile to decrypt / de-obfuscate the packet, and get the actual clear-text data

3) some local proxy processing and policies

4) decides for forward the packet to C

5) use the "C" profile to encrypt / obfuscate the clear-text data, to get data to put into a  packet

6) send the packet to C

  So anything that happens A->B doesn't affect any traffic being sent B->C.

> This security difference would also apply to storing or transmitting raw RADIUS packets for logging or debugging.  With RadSec, more sensitive data would essentially be in clear text  in those packets, perhaps including passwords.

  The packets are already in clear-text on the server.  The packets are only protected "on the wire", by the transport protocol.

  So RADIUS/UDP has exactly this problem:  all logging, debugging, etc. is done with the clear-text passwords available to the server.  Implementations have to be careful how they manage those secrets.

  Alan DeKok.