CVE-2020-26140: Alfa Awus036h Firmware RCE Vulnerability

CVE-2020-26140 Overview

CVE-2020-26140 is a significant wireless security vulnerability affecting Wi-Fi implementations across multiple vendors including ALFA, Siemens, Arista, Cisco, and Intel. The vulnerability exists in the WEP, WPA, WPA2, and WPA3 implementations which incorrectly accept plaintext frames in a protected Wi-Fi network. This flaw allows an adversary to inject arbitrary data frames independent of the network configuration, effectively bypassing the encryption protections that users expect from secured wireless networks.

This vulnerability is part of a larger collection of Wi-Fi security flaws known as "FragAttacks" (fragmentation and aggregation attacks), which were discovered through systematic analysis of the IEEE 802.11 standard and its various implementations.

Critical Impact

Attackers within radio range can inject arbitrary network frames into protected Wi-Fi networks, potentially enabling man-in-the-middle attacks, data injection, and network compromise without needing to know the Wi-Fi password.

Affected Products

• ALFA AWUS036H with Windows 10 driver version 6.1316.1209
• Siemens SCALANCE W series industrial wireless devices (W1748-1, W1750D, W1788 series, W721-1, W722-1, W734-1, W738-1, W748-1, W761-1, W774-1, W778-1, W786 series, W788 series, WAM763-1, WAM766-1, WUM763-1, WUM766-1)
• Arista C-series, O-series, and W-series access points (C-65 through C-260, O-90, O-105, W-68, W-118)
• Cisco Aironet access points (1532, 1542, 1552, 1560 series, 1572, 1702, 1800 series, 2702, 2800 series, 3702, 3800 series, 4800)
• Cisco Catalyst 9100 series access points (9105, 9115, 9117, 9120, 9124, 9130)
• Cisco Meraki MR and MX series wireless devices
• Cisco IP Phones with Wi-Fi capability (6861, 8821, 8832, 8861, 8865)
• Cisco Webex Board and Room devices
• Intel Wi-Fi adapters (AC 8260, AC 8265, AC 9260, AC 9560, Killer AC 1550, Killer Wi-Fi 6 AX1650, Killer Wi-Fi 6E AX1675)
• Intel ProSet Wi-Fi adapters (AC 3165, AC 3168, AC 8260, AC 8265, AC 9260, AC 9461, AC 9462, AC 9560, Wi-Fi 6 AX200, Wi-Fi 6 AX201, Wi-Fi 6E AX210)

Discovery Timeline

• May 11, 2021 - CVE-2020-26140 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-26140

Vulnerability Analysis

This vulnerability stems from a fundamental implementation flaw in how affected Wi-Fi devices handle frame authentication and encryption verification. In a properly secured Wi-Fi network using WEP, WPA, WPA2, or WPA3, all data frames should be encrypted and authenticated. However, vulnerable implementations fail to properly validate that incoming frames are encrypted as expected, allowing plaintext frames to be processed alongside encrypted traffic.

The attack exploits the weakness by requiring the attacker to be within radio range of the target network. From this position, the attacker can transmit specially crafted plaintext frames that the vulnerable access point or client will accept and process as legitimate network traffic. This can be accomplished without the attacker knowing the network's pre-shared key or having any authenticated association with the network.

The impact is primarily on data integrity, as attackers can inject malicious content into the network stream. This could enable scenarios such as injecting DNS responses to redirect traffic, inserting malicious content into unencrypted HTTP streams, or conducting other man-in-the-middle style attacks.

Root Cause

The root cause is classified under CWE-327 (Use of a Broken or Risky Cryptographic Algorithm). The vulnerable implementations do not properly enforce that all frames in a protected network must be encrypted. The IEEE 802.11 standard specifies encryption requirements, but certain implementations failed to reject plaintext frames when operating in protected mode, creating a gap between the security policy and actual enforcement.

Attack Vector

The attack requires adjacent network access, meaning the attacker must be within Wi-Fi radio range of the target network or device. The attack can be executed with the following characteristics:

• Access Required: Adjacent network (within radio range)
• Complexity: Low - no special conditions or timing requirements
• Privileges Required: None - attacker does not need authentication
• User Interaction: None - attack is passive from victim's perspective

An attacker positions themselves within range of the target Wi-Fi network and begins transmitting crafted plaintext 802.11 data frames. The vulnerable receiver processes these frames despite them lacking encryption, allowing the attacker to inject arbitrary data into the network communication path. This could be used to inject malicious DNS responses, TCP packets, or other network-layer attacks.

Detection Methods for CVE-2020-26140

Indicators of Compromise

• Unexpected plaintext 802.11 data frames detected within encrypted Wi-Fi networks
• Anomalous traffic patterns suggesting frame injection attacks
• DNS response anomalies indicating potential redirection attacks
• Wireless intrusion detection system alerts for protocol violations

Detection Strategies

• Deploy wireless intrusion detection systems (WIDS) capable of identifying plaintext frames in protected networks
• Monitor for 802.11 frame anomalies using specialized wireless security monitoring tools
• Implement network-level monitoring to detect unexpected traffic patterns or DNS anomalies
• Review access point and client logs for indicators of connection manipulation

Monitoring Recommendations

• Enable verbose logging on enterprise wireless controllers and access points
• Deploy sensors capable of monitoring 802.11 frame-level traffic for protocol violations
• Implement DNS security monitoring to detect potential injection attacks
• Correlate wireless monitoring data with network-level intrusion detection systems

How to Mitigate CVE-2020-26140

Immediate Actions Required

• Inventory all affected wireless devices across the network infrastructure
• Apply firmware updates from respective vendors (Cisco, Siemens, Intel, Arista, ALFA)
• Prioritize patching of publicly accessible or high-value network segments
• Enable additional encryption layers (VPN, TLS) for sensitive communications as defense-in-depth

Patch Information

Multiple vendors have released security updates to address this vulnerability:

• Cisco: Security patches are available for affected Aironet, Catalyst, Meraki, and other wireless products. See the Cisco Security Advisory for specific version information.
• Siemens: Firmware updates are available for SCALANCE W series devices. Refer to the Siemens Security Advisory SSA-913875 for details.
• Intel: Driver updates are available for affected Wi-Fi adapters through Intel's driver download center.
• Arista: Security patches are available as documented in Arista Security Advisory #12602.

Additional technical details about the FragAttacks vulnerability collection can be found at the FragAttacks Project Website and the GitHub FragAttacks Summary.

Workarounds

• Implement VPN or additional TLS encryption for all sensitive network communications as defense-in-depth
• Reduce wireless coverage area to limit attacker proximity opportunities where feasible
• Enable enterprise-grade wireless intrusion prevention capabilities if available
• Consider network segmentation to isolate critical systems from wireless attack surfaces

# Example: Verify firmware version on Cisco Aironet (IOS-XE)
show version | include System image
show inventory

# Example: Check Intel wireless driver version on Windows
netsh wlan show drivers | findstr "Driver"

# Example: Review wireless security settings
show wlan summary
show ap config general