**IKE is a type of ISAKMP** (Internet Security Association Key Management Protocol) implementation, which is a framework for authentication and key exchange. IKE establishes the security association (SA) between two endpoints through a three-phase process:
* **Phase 1:** Establish a secure channel between 2 endpoints using a Pre-Shared Key (PSK) or certificates. It can use main mode (3 pairs of messages) or **aggresive** mode.
* **Phase1.5:** This is optional, is called Extended Authentication Phase and authenticates the user that is trying to connect (user+password).
* **Phase2:** Negotiates the parameter for the data security using ESP and AH. It can use a different algorithm than the one used in phase 1 (Perfect Forward Secrecy (PFS)).
Starting Nmap 5.51 (http://nmap.org) at 2011-11-26 10:56 IST
Nmap scan report for 172.16.21.200
Host is up (0.00036s latency).
PORT STATE SERVICE
500/udp open isakmp
MAC Address: 00:1B:D5:54:4D:E4 (Cisco Systems)
```
## **Finding a valid transformation**
The IPSec configuration can be prepared only to accept one or a few transformations. A transformation is a combination of values. **Each transform** contains a number of attributes like DES or 3DES as the **encryption algorithm**, SHA or MD5 as the **integrity algorithm**, a pre-shared key as the **authentication type**, Diffie-Hellman 1 or 2 as the key **distribution algorithm** and 28800 seconds as the **lifetime**.
Then, the first thing that you have to do is** find a valid transformation**, so the server will talk to you. To do so, you can use the tool **ike-scan**. By default, Ike-scan works in main mode, and sends a packet to the gateway with an ISAKMP header and a single proposal with **eight transforms inside it**.
As you can see in the previous response, there is a field called **AUTH** with the value **PSK**. This means that the vpn is configured using a preshared key (and this is really good for a pentester).\
* _**1 returned handshake; 0 returned notify**_**: **This means the **target is configured for IPsec and is willing to perform IKE negotiation, and either one or more of the transforms you proposed are acceptable** (a valid transform will be shown in the output)
* _0 returned handshake; 1 returned notify:_ VPN gateways respond with a notify message when **none of the transforms are acceptable** (though some gateways do not, in which case further analysis and a revised proposal should be tried).
Then, in this case we already have a valid transformation but if you are in the 3rd case, then you need to **brute-force a little bit to find a valid transformation:**
First of all you need to create all the possible transformations:
```bash
for ENC in 1 2 3 4 5 6 7/128 7/192 7/256 8; do for HASH in 1 2 3 4 5 6; do for AUTH in 1 2 3 4 5 6 7 8 64221 64222 64223 64224 65001 65002 65003 65004 65005 65006 65007 65008 65009 65010; do for GROUP in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18; do echo "--trans=$ENC,$HASH,$AUTH,$GROUP" >> ike-dict.txt ;done ;done ;done ;done
while read line; do (echo "Valid trans found: $line" && sudo ike-scan -M $line <IP>) | grep -B14 "1 returned handshake" | grep "Valid trans found" ; done <ike-dict.txt
```
If the brute-force didn't work, maybe the server is responding without handshakes even to valid transforms. Then, you could try the same brute-force but using aggressive mode:
```bash
while read line; do (echo "Valid trans found: $line" && ike-scan -M --aggressive -P handshake.txt $line <IP>) | grep -B7 "SA=" | grep "Valid trans found" ; done <ike-dict.txt
Cisco recommends avoidance of DH groups 1 and 2 in particular. The paper’s authors describe how it is likely that **nation states **can **decrypt****IPsec **sessions negotiated using **weak groups **via discrete log **precomputation**. The hundreds of millions of dollars spent performing precomputation are amortised through the real-time decryption of any session using a weak group (1,024-bit or smaller).
Then, you can use ike-scan to try to **discover the vendor** of the device. The tool send an initial proposal and stops replaying. Then, it will **analyze** the **time** difference **between** the received **messages** from the server and the matching response pattern, the pe tester can successfully fingerprint the VPN gateway vendor. More over, some VPN servers will use the optional **Vendor ID (VID) payload** with IKE.
If **no hash is returned**, then probably this method of brute forcing** will work**. If **some****hash **is returned, this means that a **fake hash is going to be sent** back for a fake ID, so **this method won't be reliable** to brute-force the ID. For example, a fake hash could be returned (this happens in modern versions):
If you have discovered an specific transformation add it in the ike-scan command. And if you have discovered several transformations feel free to add a new loop to try them all (you should try them all until one of them is working properly).
You can use the[ dictionary of ikeforce](https://github.com/SpiderLabs/ikeforce/blob/master/wordlists/groupnames.dic) or [the one in seclists](https://github.com/danielmiessler/SecLists/blob/master/Miscellaneous/ike-groupid.txt) of common group names to brute-force them:
[** iker.py**](https://github.com/isaudits/scripts/blob/master/iker.py)** **also uses **ike-scan** to bruteforce possible group names. It follows it's own method to **find a valid ID based on the output of ike-scan**.
[ikeforce.py](https://github.com/SpiderLabs/ikeforce) is a tool that can be used to **brute force IDs also**. This tool will **try to exploit different vulnerabilities** that could be used to **distinguish **between a **valid **and a** non-valid ID** (could have false positives and false negatives, that is why I prefer to use the ike-scan method if possible).
* The **first method** is to brute-force the group names by **searching** for the information **Dead Peer Detection DPD** of Cisco systems (this info is only replayed by the server if the group name is correct).\
* The **second method** available is to **checks the number of responses sent to each try** because sometimes more packets are sent when the correct id is used.\
* The **third method** consist on **searching for "INVALID-ID-INFORMATION" in response to incorrect ID**.\
* Finally, if the server does not replay anything to the checks, **ikeforce** will try to brute force the server and check if when the correct id is sent the server replay with some packet.\
Obviously, the goal of brute forcing the id is to get the **PSK** when you have a valid id. Then, with the **id** and **PSK** you will have to bruteforce the XAUTH (if it is enabled).
If you have discovered an specific transformation add it in the ikeforce command. And if you have discovered several transformations feel free to add a new loop to try them all (you should try them all until one of them is working properly).
It is also possible to obtain valid usernames by sniffing the connection between the VPN client and server, as the first aggressive mode packet containing the client ID is sent in the clear (from the book **Network Security Assessment: Know Your Network**)
Finally, If you have find a **valid transformation** and the** group name** and the **aggressive mode is allowed**, then you can very easily grab the crackable hash:
Most implementations use** aggressive mode IKE with a PSK to perform group authentication**, and **XAUTH **to provide additional** user authentication** (via Microsoft Active Directory, RADIUS, or similar). Within **IKEv2**, **EAP replaces XAUTH** to authenticate users.
So you can capture the data of the login using _fiked_ and see if there is any default username (You need to redirect IKE traffic to `fiked` for sniffing, which can be done with the help of ARP spoofing, [more info](https://opensourceforu.com/2012/01/ipsec-vpn-penetration-testing-backtrack-tools/)). Fiked will act as a VPN endpoint and will capture the XAuth credentials:
Also, using IPSec try to make a MitM attack and block all traffic to port 500, if the IPSec tunnel cannot be established maybe the traffic will be sent in clear.
### Brute-forcing XAUTH username ad password with ikeforce
To brute force the **XAUTH** (when you know a valid group name **id** and the **psk**) you can use a username or list of usernames and a list o passwords:
In Kali **VPNC **is used to establish IPsec tunnels. The **profiles **have to be located in _**/etc/vpnc/**_** **and you can use the tool _**vpnc **_to call them.\
