A weakness exists in TKIP that can allow an attacker to decrypt packets
under certain circumstances. This is not a key recovery attack. The attacker
can only recover the key used to authenticate packets but not the key used to
encrypt and obfuscate data. With the recovered key, only captured packets may
be forged in a limited window of at most 7 attempts. The attacker can only
decrypt one packet at a time, currently at a rate of one packet per 12-15
minutes. Additionally, packets can only be decrypted when sent from the
wireless access point (AP) to the client (unidirectional). Only devices
configured to use TKIP as the encryption mechanism are affected by these
attacks. Customers who use WPA2 with the AES-CCMP cipher suite are not
vulnerable to these attacks.
AES is a more secure encryption algorithm and has been deemed
acceptable for the US government to encrypt both non-classified and classified
data. At this time, there are no known successful attacks to break an AES
encryption key. AES is the current highest standard for encryption, and
replaces WEP; therefore, the use of WPA2 with AES is recommended whenever
possible. Its predecessor, WPA, was an interim protocol. The majority of recent
wireless devices and clients support the AES encryption standard.
Note: For a list of WPA2-supported clients, please visit
If a client does not support WPA2 with AES due to age of the hardware
or lack of driver compatibility, a VPN is the next best solution for securing
over-the-air client connections. A VPN combined with network segmentation using
multiple SSIDs and VLANs provides a robust solution for networks with varied
clients. IP Security (IPSec) and Secure Sockets Layer (SSL) VPNs provide a
similar level of security as WPA2.
The following workarounds and mitigations are available when WPA2 with
AES is not available.
Workarounds and Mitigations
To mitigate this issue, users are advised to rotate the pairwise key
more frequently. While it has been suggested that 120 seconds be the rekey
interval, using a rotation interval of 300 seconds should be sufficient in most
environments as the attacker must take on the order of 8 minutes or longer to
recover the partial key, a longer interval may still be adequate and would
result in less of a load on the RADIUS server.
Caution: Decreasing the key rotation interval will increase the load on the
RADIUS server if using EAP.
On Autonomous APs the dot1x timeout reauth-period
<nSeconds> command can be used to
modify the key rotation interval.
Note: This command can be used globally per AP; per wireless domain
services (WDS); or as provided from a RADIUS server, depending on the
On the Wireless LAN Controller (WLC) web console navigate to
WLANs > Advanced > Enable Session Timeout.
Alternatively, the config wlan session-timeout
<nSeconds> command line interface
(CLI) command can be used to modify the key rotation interval.
Disabling WMM is still being investigated as a viable workaround on
Message Integrity Check (MIC) errors incorporated in Wi-Fi Protected
Access (WPA) are not necessarily indicative of an attack; in fact, various
clients, such as Cisco 7920 phones, are known to occasionally generate MIC
errors in normal operation. However, a carefully executed instance of this
attack will generate MIC errors at a rate of less than once per minute, to
prevent triggering AP countermeasures. The following is an example of the
Wireless LAN Controller (WLC) system message seen when AP countermeasures have
The AP '00:0b:85:67:6b:b0' received a WPA MIC
error on protocol '1' from Station '00:13:02:8d:f6:41'.
Counter measures have been activated and traffic has
been suspended for 60 seconds.
This error may indicate that someone in the network is attempting to
replay the message that was sent by the original client, or that the client is
faulty. If a client repeatedly fails the MIC check, the controller disables
that WLAN for 60 seconds as per the WPA protocol requirements. This prevents a
possible attack on the encryption scheme. These MIC errors cannot be turned off
on the controllers. For more information refer to the Wireless LAN Controller
(WLC) Error and System Messages FAQ at the following link: