CVE-2025-71127: Linux Kernel Auth Bypass Vulnerability

CVE-2025-71127 Overview

A vulnerability has been identified in the Linux kernel's mac80211 WiFi subsystem that allows attackers to bypass beacon protection mechanisms. The flaw exists in the handling of Beacon frames, where frames sent to unicast (non-broadcast) addresses are improperly processed when the Protected Frame bit is set. According to IEEE Std 802.11-2020, Section 11.1.3.1, Beacon frames must be sent to the broadcast address. However, the current implementation fails to properly validate this requirement, particularly when beacon protection is enabled.

The vulnerability allows an attacker within wireless range to craft malicious unicast Beacon frames that bypass beacon protection checks. This could be exploited to perform targeted attacks against associated stations (STAs), such as using Channel Switch Announcement (CSA) to forcibly move a client to another channel, potentially facilitating further attacks like denial of service or man-in-the-middle scenarios.

Critical Impact

Attackers within wireless range can bypass beacon protection mechanisms to manipulate associated WiFi stations, potentially forcing channel changes or disrupting wireless connectivity.

Affected Products

• Linux kernel with mac80211 WiFi subsystem
• Systems using WiFi beacon protection (BIGTK)
• Wireless network infrastructure running vulnerable kernel versions

Discovery Timeline

• 2026-01-14 - CVE CVE-2025-71127 published to NVD
• 2026-01-19 - Last updated in NVD database

Technical Details for CVE-2025-71127

Vulnerability Analysis

The vulnerability resides in the mac80211 subsystem's beacon frame processing logic. The IEEE 802.11 standard mandates that Beacon frames use the broadcast address in the Address 1 (A1) field. However, the Linux kernel's implementation contains a flaw in how it validates beacon frames when beacon protection is enabled.

When a unicast Beacon frame arrives with the Protected Frame bit set to 0, the current implementation correctly discards it. However, when the Protected Frame bit is set to 1, the validation logic for checking configured BIGTK (Beacon Integrity Group Temporal Key) fails to properly function. This allows unicast Beacon frames with the Protected Frame bit enabled to be accepted as valid, even though they are not actually protected.

This creates a security gap where an attacker can craft unicast Beacon frames that appear to use beacon protection but actually bypass the authentication and integrity checks entirely.

Root Cause

The root cause is improper input validation in the mac80211 beacon frame processing code. The logic path for validating beacon protection when the Protected Frame bit is set to 1 does not properly check for unicast destination addresses before proceeding with BIGTK verification. This allows unprotected unicast beacon frames to slip through validation when they should be rejected based on the non-broadcast destination address alone.

The fix addresses this by implementing a more generic check that discards all Beacon frames based on a simple condition: if Address 1 (A1) contains a unicast address rather than the broadcast address, the frame is dropped immediately, regardless of the Protected Frame bit state.

Attack Vector

An attacker operating within wireless range of target stations can exploit this vulnerability by:

1. Crafting malicious Beacon frames with a unicast destination address targeting a specific associated station
2. Setting the Protected Frame bit to 1 to bypass the existing unicast beacon filtering
3. Including malicious payload such as Channel Switch Announcement (CSA) elements
4. Transmitting the crafted frames to manipulate the target station's behavior

The attack requires proximity to the wireless network but does not require authentication to the network. The attacker can use this to force targeted stations to switch channels, potentially disrupting connectivity or positioning them for further attacks on a controlled channel.

Detection Methods for CVE-2025-71127

Indicators of Compromise

• Unusual wireless frame activity with unicast Beacon frames detected in wireless traffic captures
• Unexpected channel switching behavior on client stations without administrator-initiated changes
• Wireless IDS/IPS alerts for malformed or non-compliant 802.11 beacon frames
• Client devices experiencing intermittent connectivity issues or unexpected disconnections

Detection Strategies

• Deploy wireless intrusion detection systems (WIDS) configured to alert on beacon frames with unicast destination addresses
• Monitor wireless traffic using packet capture tools like tcpdump or Wireshark, filtering for Beacon frames where the A1 field is not ff:ff:ff:ff:ff:ff
• Implement kernel-level auditing to detect anomalies in mac80211 subsystem behavior
• Review system logs for wireless driver warnings related to beacon frame processing

Monitoring Recommendations

• Enable verbose logging for the mac80211 subsystem to capture frame processing details
• Configure centralized logging for wireless infrastructure to correlate suspicious activity across access points
• Monitor for patterns of CSA activity that do not correspond to legitimate administrative actions
• Implement network-based detection for 802.11 frame anomalies at the wireless controller level

How to Mitigate CVE-2025-71127

Immediate Actions Required

• Update the Linux kernel to a patched version that includes the mac80211 beacon frame validation fix
• If driver-level beacon filtering is available, ensure it is enabled to drop unicast beacon frames
• Review wireless network configurations and ensure beacon protection (BIGTK) is properly configured where supported
• Monitor wireless environments for suspicious beacon frame activity until patches can be applied

Patch Information

The Linux kernel developers have released patches to address this vulnerability across multiple stable kernel branches. The fix implements strict filtering that discards all Beacon frames sent to non-broadcast addresses, providing a comprehensive solution that covers all attack scenarios regardless of the Protected Frame bit state.

Patches are available through the following kernel commits:

• Linux Kernel Commit 0a59a38
• Linux Kernel Commit 193d18f
• Linux Kernel Commit 6e5bff4
• Linux Kernel Commit 7b240a8
• Linux Kernel Commit 88aab15
• Linux Kernel Commit a21704d
• Linux Kernel Commit be0974b

Workarounds

• If kernel updates cannot be immediately applied, consider enabling driver-level beacon filtering where supported by the wireless hardware
• Implement wireless intrusion prevention systems to actively block malformed beacon frames
• Restrict physical access to wireless coverage areas to limit attacker proximity
• Consider temporarily disabling beacon protection if the environment does not require it, as this changes the attack surface (note: this reduces overall security and should only be a temporary measure)

# Check current kernel version for vulnerability assessment
uname -r

# Monitor for unicast beacon frames using tcpdump (detection only)
tcpdump -i wlan0 -e 'type mgt subtype beacon' | grep -v 'ff:ff:ff:ff:ff:ff'

# Update kernel on Debian/Ubuntu systems
sudo apt update && sudo apt upgrade linux-image-$(uname -r)

# Update kernel on RHEL/CentOS systems
sudo yum update kernel