Draft:Caffe Latte Attack in Wireless Networks

For the coffee beverage, see Caffè latte.

Caffe Latte attack is a client-side cryptographic attack against Wired Equivalent Privacy (WEP) that enables an attacker to recover a network’s WEP key by interacting directly with a Windows-based wireless client, even when the attacker is not within radio range of the target access point (AP). The attack exploits weaknesses in WEP’s design and the behavior of the Microsoft Windows wireless stack to generate sufficient encrypted traffic (e.g., ARP frames) for statistical key recovery, typically within minutes.

Overview

WEP is a deprecated security algorithm for IEEE 802.11 wireless networks that uses the stream cipher RC4 for confidentiality and CRC-32 for integrity. Its 24-bit initialization vector (IV) and RC4 key scheduling weaknesses allow practical key recovery via passive and active techniques, including ARP replay and IV-based statistical attacks. The Caffe Latte attack extends earlier WEP-breaking methods by targeting a roaming client (e.g., a laptop) to induce encrypted traffic and recover the WEP key without requiring a direct connection to the protected AP.

Background

Early WEP attacks relied on collecting large numbers of encrypted frames within range of the target AP to exploit RC4 IV weaknesses and recover pre-shared keys. Subsequent research demonstrated active traffic generation (ARP replay) and protocol-level exploits that accelerated key recovery. The Caffe Latte attack addresses scenarios where the target AP is not reachable but a previously authenticated client can be coerced into generating WEP-encrypted traffic elsewhere, such as a public hotspot.

Attack model

The attacker sets up a rogue AP or uses a wireless interface to communicate directly with the client’s Windows wireless stack. By sending crafted frames (notably encrypted ARP requests), the attacker triggers the client to respond with WEP-encrypted packets using cached credentials for the original WEP network. These responses, combined with repeated replays, provide sufficient IV diversity and keystream material to mount standard WEP key recovery.

Prerequisites

• The client must have previously connected to a WEP-protected SSID and still retain the WEP key material (e.g., via profile caching in the Windows wireless stack).
• The attacker must be able to interact with the client’s wireless interface (e.g., in a public location), even if the target AP is out of range.
• The client must accept frames from a nearby radio (e.g., association or data exchange via a rogue AP or ad hoc interaction).

Procedure

1. Establish proximity to the client device and initiate a rogue association or lure the client into exchanging frames.
2. Inject or replay encrypted ARP requests targeting the client to stimulate responses.
3. Capture the client’s WEP-encrypted responses and collect sufficient packets to exploit IV repetition and RC4 weaknesses.
4. Apply statistical key recovery techniques to derive the WEP key from the captured traffic.

Time to recovery

Reported demonstrations recovered WEP keys within minutes (often under six minutes) given favorable conditions and a responsive client.

Technical basis

WEP’s use of RC4 with a short (24-bit) IV facilitates keystream reuse and enables practical attacks when large numbers of frames can be captured or actively generated. Windows client behavior may permit responses to injected frames using cached WEP credentials, allowing attackers to harvest keystreams remotely from clients rather than APs.

Relation to other WEP attacks

• ARP replay: Active generation of traffic to accelerate IV collection; the Caffe Latte attack applies similar principles against clients.
• Fragmentation-based exploitation: Protocol-level manipulation to make earlier attacks practical in the field.
• Shared Key authentication leakage: Deriving keystreams from challenge–response exchanges; relevant to stimulating traffic during client-side attacks.

Impact and risk

The Caffe Latte attack increases risk exposure for mobile users and enterprises by enabling WEP key recovery far from the protected environment. A compromised key permits the attacker to join the WEP network when in range, decrypt traffic, inject packets, and pivot to other systems. Because the attack targets clients, traditional AP-centered defenses may be ineffective if WEP remains in use on any managed or unmanaged SSIDs.

Countermeasures

• Migrate from WEP to WPA/WPA2 (with AES/CCMP), or WPA3 where supported.
• Disable WEP profiles and remove cached credentials on client devices; audit preferred networks for legacy WEP entries.
• Client hardening: Apply OS and driver updates, disable automatic association to unknown SSIDs, and enforce 802.1X/EAP where possible.
• Use encrypted tunnels (e.g., IPsec, SSH, TLS) when traversing untrusted networks, noting that this does not remedy WEP’s weaknesses but protects upper-layer traffic.
• Policy controls and compliance: Industry standards (e.g., PCI DSS) prohibit WEP in payment environments; enforce configuration baselines accordingly.

History

The attack was publicly described by security researchers and vendors during the mid‑2000s as part of broader demonstrations of WEP’s systemic weaknesses and client-side exposure. Coverage included technical tutorials and vendor advisories detailing exploitation steps and mitigations.

Legal and ethical considerations

Unauthorized interception of communications and access to protected networks may be illegal under computer misuse and telecommunications laws. Security testing requires explicit authorization and adherence to organizational policy and applicable regulations.

See also

• Wired Equivalent Privacy
• ARP spoofing
• Man-in-the-middle attack
• Wireless security
• RC4

External links

• "Intercepting Mobile Communications: The Insecurity of 802.11" (PDF). ACM MobiCom (archived). Archived from the original (PDF) on 1 October 2006. Retrieved 2025-10-21.
• "The Final Nail in WEP's Coffin" (PDF). IEEE S&P (archived). Retrieved 2025-10-21.
• "WEP Key Recovery Tools (aircrack-ng)". Retrieved 2025-10-21.