IPsec Client VPN - aggressive mode

[marstoyanoff]

Hi all,

I just got off the phone with customer that has passed a security scan check from a third party vendor. One of the vulnerebilities mentioned in the report is as follows:

I know that only the IPsec client VPN uses aggressive mode to negotiate Phase I. So my question is how can I convince my customer to continue using the IPsec VPN? Is there anything I can do to reduce the risk of using this type of remote accesses. Also, am I having the same issue if I use SSL Client based VPN?

Regards,

Marty

[malshbou]

Hi,

IKE agressive mode has the well-known vulnerability of exchanging identities in cleartext.

You can use certificate authentication instead of pre-shared keys, or you can migrate to SSL VPN that doesn't have the agressive mode vulnerability.

Hope this helps

Mashal

[olpeleri · Accepted solution]

Hello,

Ikev1 HUB running aggressive mode sends his PSK hash in the second packet along with his DH public value.

That's indeed a well-know protocol weakness.

To be able to act on that, U would have to be on the path to capture this flow in order to brute force the hash [ which is not obvious - but not impossible]

This issue is seriously mitigated by enabling XAUTH [User authentication].

Xauth is happening after DH , therefore under encryption.

Assuming strong password policy is in use, it's then very very very complex to find the right combination of user/password.

Ikev2 is way more secure in that regard and it's the right path.

Cheers,

Olivier

[marstoyanoff]

Thank you guys!

Cheers

Marty

[Javier Portuguez · Accepted solution]

I totally agreed with Olivier

Here is some information for future reference:

IPsec client (legacy):

ASA/PIX 8.x and VPN Client IPSec Authentication Using Digital Certificates with Microsoft CA Configuration Example

Configuring IPSec Between Cisco IOS Routers and Cisco VPN Client Using Entrust Certificates

Digital Certificates/PKI for IPSec VPNs

AnyConnect:

ASA 8.4+ Configuring AnyConnect VPN Client Connections

ASA 8.4+ AnyConnect IKEv2

IOS FlexVPN Deployment: AnyConnect IKEv2 Remote Access with EAP-MD5

HTH.

Portu.

[marstoyanoff]

The links are fantastic. Thank Javier!

[Javier Portuguez]

You are welcome!!

Please rate any helpful posts and mark this post as answered

[vikaspurohit1]

Hello Javier,

I believe this vulnerability does not impact site to site VPNs.. specially when we are running over MPLS cloud instead of internet.. please confirm. I am facing a similar situation and need to present solution to customer security board.

[Javier Portuguez]

Hello,

Yes you are correct. The reason for that is because LAN-to-LAN tunnels with pre-shared-keys use ISAKMP Main Mode.

So the key is protected during the exchange.

HTH.