incorrect shared secret entry authenticates successfully forfreerradius

[Michael Lecuyer]

NTRadPing is a very bad client to test real authentication.

While it says it has an Access-Accept packet it isn't doing any proper 
checking of the packet. All Access-Accept packets are signed by the 
server using the shared secret. A good client will check that signature. 
A packet with a bad signature is rejected by a proper client even though 
the server sent an Access-Accept.

Your test and discussion are pointless because the client NTRadPing is 
not telling you that the packet is invalid. It's just displaying the 
packet's contents.

PAP is the only authentication method where you would get an 
Access-Reject with a bad secret.

sanjeev.kumarroy at wipro.com wrote:
> Hi Phil,
> I checked the issue with MSCHAP v1 and v2 as well. Even there the
> authentication passes for an incorrect secret key
> 
> Thanks
> 
> -----Original Message-----
> From:
> freeradius-users-bounces+sanjeev.kumarroy=wipro.com at lists.freeradius.org
> [mailto:freeradius-users-bounces+sanjeev.kumarroy=wipro.com at lists.freera
> dius.org] On Behalf Of Phil Mayers
> Sent: Tuesday, March 18, 2008 7:24 PM
> To: FreeRadius users mailing list
> Subject: Re: incorrect shared secret entry authenticates successfully
> forfreerradius
> 
> sanjeev.kumarroy at wipro.com wrote:
>> Hi,
>> I am using the following configuration:
>>
>> O/S: rhel4_u5_i386
>> Freeradius 1.1.7 
>> Client to test: NTRadPing 1.5
>>
>> Steps undertaken:
>> --------------------
>> - Installed a fresh system with rhel4_u5_i386
>> - Build and compile freeradius 1.1.7 on it.
>> - Update the clients.conf file to add the client entries for the
> machine
>> that uses NTRadPing 1.5 (IP of the client machine and the shared
> secret)
>> - Start the radiusd daemon in debug mode (radiusd -X)
>> - Now generate a simple PAP authentication request using NTRadPing.
>> (Port is 1812, also provide the shared secret correctly). The
>> authentication passes successfully as it should. Now give a junk
> secret
>> key in the NTRadPing utility. The access is rejected.
>> - However when the same cases are tried for CHAP we can see the
>> difference. In the first case the authentication is successful;
> however
>> when we give a junk shared secret the authentication should ideally
> have
>> been rejected. However the authentication passes successfully.
>> NOTE: I tried the same for MSCHAPv1 and MSCHAPv2 authentication using
>> VPN client. There I can see clearly that the access is not granted to
>> the VPN client. However when we look at the radius logs it can be seen
>> that the Authentication requests responds with a Successful message.
>>
>> Any help or info in this regards would be highly appreciated.
> 
> Only certain radius AVPs are encrypted with the shared secret:
> 
> fgrep encrypt /usr/share/freeradius/dictionary*
> 
> User-Password is one, so PAP fails if the shared secret is wrong. The 
> CHAP attributes are not, so the request succeeds. The MS-CHAP-MPPE-Keys 
> or MS-MPPE-Send-Key/MS-MPPE-Recv-Key reply attributes are encrypted, so 
> MS-CHAP will fail.
> 
> Many recent radius clients support the Message-Authenticator attribute, 
> which is a signature over the entire packets AVPs encrypted with the 
> shared secret. This will cause incorrect shared secrets to reject an 
> entire packet. See section 3.2 of RFC3579.
> 
> If your NAS supply Message-Authenticator, you could refuse packets 
> without one:
> 
> DEFAULT	Message-Authenticator !* ANY, Auth-Type := Reject
> 
> 
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