12.1 Weak and Deprecated WLAN Security

CWNA-109 Domain 5 is only 10 percent of the scored exam, but a WLAN that trusts a broken control is a failed deployment no matter how clean the RF design looks. Objective 5.1 asks you to identify weak security options that should not be used in enterprise WLANs and to explain why each one is insufficient. This OpenExamPrep chapter teaches those options the way an administrator meets them on a controller or autonomous AP: WEP, 802.11 Shared Key authentication, SSID hiding sold as a security mechanism, MAC filtering, and deprecated WPA and/or WPA2 with TKIP.

The skill is judgment, not an attack lab. You should be able to open a WLAN profile, name the failure mode, and replace the control with AES-based encryption plus a real identity method (WPA2-Enterprise or WPA3), which later sections develop. Do not treat “extra checkboxes” as defense in depth when the checkbox itself is the vulnerability.

WEP is not a confidentiality service you can salvage

Wired Equivalent Privacy (WEP) was the original IEEE 802.11-1999 confidentiality service. It used the RC4 stream cipher with a static secret concatenated to a 24-bit initialization vector (IV). Product marketing called the result 64-bit or 128-bit WEP; the secret itself was only 40 bits or 104 bits. Integrity was a CRC-32 Integrity Check Value (ICV). CRC-32 is an error-detecting checksum. It is not a cryptographic message integrity code. An adversary who can modify ciphertext can often induce a matching change in recovered plaintext and then recompute a CRC that still looks valid to the receiver.

Because RC4 is a stream cipher, reusing an IV with the same secret reuses a keystream. A busy BSS consumes the 24-bit IV space in ordinary production traffic, so reuse is an operational certainty rather than a rare corner case. The small IV space and RC4’s key-scheduling behavior also created classes of weak IVs that leak information about the static secret. WEP used one shared key for every station. There is no per-user identity, no per-session key, and no way to revoke a lost laptop without rekeying the entire BSS.

IEEE and the Wi-Fi Alliance retired WEP. Many vendors have removed the option; others still expose it for antique scanners. Enterprise policy is binary: if WEP is enabled on any SSID that can reach a production VLAN, that SSID is not an enterprise WLAN. There is no “WEP with a long key,” no “WEP plus MAC filter,” and no “WEP for IoT only” exception that restores confidentiality. Replace the SSID’s cipher with AES-CCMP (or a WPA3 suite) and put authentication in 802.1X or SAE.

Shared Key authentication is worse than Open System

IEEE 802.11 defined two authentication algorithms: Open System and Shared Key. Shared Key is a WEP challenge-response. The AP sends a challenge in the clear. The station encrypts that challenge with the WEP key and returns ciphertext. A successful exchange proves the station knows the WEP key—and it also hands a passive observer a known plaintext and the matching ciphertext. Combining those two values yields a keystream of that length, which is enough to forge a later Shared Key success without knowing the secret. That is why Shared Key is a weaker choice than Open System, not a stronger one.

Open System authentication is a null check: two frames, status success, no credential. That sounds insecure until you remember that Robust Security Network (RSN) authentication happens after association. Enterprise WLANs use Open System at the 802.11 authentication step, then prove identity with 802.1X/EAP or SAE and install keys with the 4-way handshake. Shared Key cannot run without WEP, so enabling it drags a deprecated cipher into the BSS. If a configuration screen still offers Shared Key, treat it as a defect and leave Open System selected so that RSN can do the real work.

Do not confuse 802.11 “authentication” frames with user login. Passing Open System only means the station is allowed to proceed to association. Passing Shared Key only means WEP was used as a broken handshake. Neither frame type is 802.1X, and neither replaces RADIUS.

SSID hiding is not a security mechanism

Hiding the SSID means suppressing the SSID string in Beacon frames so a casual scan list looks empty. That is not confidentiality and it is not authentication. The SSID still appears in Probe Request frames from clients that already know the network, in Probe Response frames, and in Association Request frames. Anyone who waits for a legitimate join with a protocol analyzer can read the name. The control is obscurity of a broadcast identifier, not access control.

Hidden SSIDs also tax operations. Clients must actively probe for a named network, which increases management airtime, complicates roaming, and breaks some consumer and IoT stacks that expect a Beacon SSID. Users then store the hidden network on every laptop. Those laptops send directed probes containing the enterprise SSID in airports and hotels, advertising which organization the traveler belongs to. Use hiding only if a designer wants less casual clutter on a scan list, and never document it as a security control. Access control belongs in AKM and cipher configuration, not in Beacon formatting.

MAC filtering does not authenticate stations

A MAC filter is an allow-list or deny-list of 48-bit 802.11 addresses. It feels like a door lock because the AP rejects unknown stations. It fails as enterprise security for three independent reasons.

First, MAC addresses in the 802.11 header are not encrypted by WEP, TKIP, CCMP, or GCMP. Those ciphers protect the frame body, not the address fields. A valid address can be observed on the air and reused by another radio. Second, the list does not scale: every BYOD phone, replacement NIC, and contractor laptop becomes a change ticket. Third, modern client operating systems randomize MAC addresses per SSID or per session, so a carefully maintained allow-list randomly blocks legitimate devices.

Filtering can still be a minor hygiene control on a lab AP with three known printers. It is not authentication, it is not a substitute for 802.1X, and it must not be the primary gate on an enterprise SSID. If you need to identify a device, use a certificate or a unique 802.1X identity, not a spoofable header field.

WPA and WPA2 with TKIP are deprecated

Wi-Fi Protected Access (WPA) was an emergency retrofit so existing WEP hardware could mix per-packet keys. Temporal Key Integrity Protocol (TKIP) still used RC4. It added a per-packet mixing function, an extended 48-bit IV, and the Michael message integrity check. Michael was deliberately lightweight so legacy CPUs could compute it. That design left TKIP with weak integrity and with countermeasures that can silence a BSS when MIC failures accumulate. TKIP was a bridge off WEP, not a destination cipher.

WPA2 made AES-CCMP the mandatory pairwise cipher and left TKIP as a compatibility option. That compatibility option is now deprecated. Configuring “WPA/WPA2 mixed,” “WPA2-TKIP,” or TKIP as the group cipher on an enterprise SSID reintroduces RC4 and Michael. It often blocks HT, VHT, and HE data rates, because 802.11n and later high-throughput PHYs expect CCMP for those rates. The Wi-Fi Alliance no longer treats TKIP as an acceptable cipher for new equipment, and WPA3 modes refuse to coexist with TKIP on the same BSS.

The exam phrase “deprecated security methods (for example WPA and/or WPA2 with TKIP)” means both original WPA-TKIP and any WPA2 profile that still selects TKIP as a unicast or group cipher. AES in the product name is not enough if TKIP remains enabled beside it. Set unicast and group ciphers to CCMP-only (or a WPA3 suite). If a warehouse scanner cannot do CCMP, isolate it on a constrained SSID with a replacement plan; do not weaken the employee SSID to match the scanner.

Why none of these controls survive enterprise requirements

Enterprise WLAN security needs per-user or per-device identity, strong confidentiality and integrity, revocation without a building-wide passphrase change, and operations that survive thousands of endpoints. WEP, Shared Key, cloaked SSIDs, MAC lists, and TKIP each fail at least two of those tests:

A useful exam habit is to ask, for every checkbox: Does this prove who the station is, or only that it can copy something from the air? WEP keys, Shared Key transcripts, Beacon formatting, and MAC headers are all copyable. Move identity into 802.1X or SAE and encryption into AES-CCMP or GCMP, which the next sections treat as the effective enterprise baseline.