CVE-2024-35845: Linux Kernel iwlwifi NUL Termination Flaw

CVE-2024-35845 Overview

CVE-2024-35845 is a critical vulnerability in the Linux kernel's Intel Wireless WiFi (iwlwifi) driver affecting the debug TLV (Type-Length-Value) handling functionality. The vulnerability exists in the iwl_fw_ini_debug_info_tlv structure which is used as a string but lacks proper NUL termination validation before use. This missing string termination check can lead to out-of-bounds memory access when the driver processes malformed firmware debug information.

Critical Impact

This vulnerability allows potential information disclosure and system crashes through network-accessible attack vectors, with no privileges or user interaction required for exploitation.

Affected Products

• Linux Kernel (multiple versions)
• Debian Linux 10.0
• Systems with Intel Wireless WiFi adapters using the iwlwifi driver

Discovery Timeline

• 2024-05-17 - CVE-2024-35845 published to NVD
• 2025-04-07 - Last updated in NVD database

Technical Details for CVE-2024-35845

Vulnerability Analysis

The vulnerability resides in the iwlwifi driver's debug TLV parsing code. The iwl_fw_ini_debug_info_tlv structure contains string data that is processed by the kernel without first verifying proper NUL termination. When firmware debug information is parsed, the driver treats this structure's contents as a C-style string, expecting it to end with a NUL character (\0). Without this termination check, memory reads can continue past the intended buffer boundary.

This is classified under CWE-134 (Use of Externally-Controlled Format String), as the string handling can be influenced by external input through the firmware interface. The network attack vector enables remote triggering without requiring local system access, authentication, or user interaction.

Root Cause

The root cause is the absence of explicit NUL termination validation in the iwlwifi debug TLV processing path. When the driver receives debug information through the iwl_fw_ini_debug_info_tlv structure, it directly uses the contained data as a string in subsequent operations. The fix ensures the string buffer is properly NUL-terminated before any string operations are performed on it.

Attack Vector

The vulnerability can be exploited through network-based attacks targeting the WiFi subsystem. An attacker could potentially craft malicious firmware debug data or manipulate wireless frames that trigger the vulnerable code path. The exploitation does not require authentication or user interaction, making it particularly dangerous in environments where affected systems are exposed to untrusted wireless networks.

The iwlwifi driver processes this debug information during normal operation, meaning any system with an Intel wireless adapter using the vulnerable driver versions could be affected. Successful exploitation could result in information disclosure from kernel memory or denial of service through system crashes.

Detection Methods for CVE-2024-35845

Indicators of Compromise

• Kernel panic or oops messages referencing the iwlwifi driver or iwl_fw_ini_debug_info_tlv
• Unexpected system crashes when WiFi is active or during wireless connection establishment
• Memory corruption warnings in kernel logs related to the wireless subsystem
• Unusual behavior of the iwlwifi driver module including repeated restarts

Detection Strategies

• Monitor dmesg and /var/log/kern.log for iwlwifi-related errors or memory access violations
• Deploy kernel live patching solutions to detect vulnerable kernel versions in production environments
• Use SentinelOne Singularity platform to monitor for kernel-level anomalies and exploit attempts
• Implement network intrusion detection rules for anomalous 802.11 traffic patterns

Monitoring Recommendations

• Enable kernel crash dump collection to capture forensic evidence of exploitation attempts
• Monitor wireless interface statistics for unusual error counts or resets
• Configure alerts for unexpected iwlwifi module reloads or failures
• Track kernel version inventories across the organization to identify vulnerable systems

How to Mitigate CVE-2024-35845

Immediate Actions Required

• Update to a patched Linux kernel version that addresses CVE-2024-35845
• If immediate patching is not possible, consider temporarily disabling WiFi on critical systems
• Review and apply vendor-specific patches from Debian and other distribution maintainers
• Prioritize patching for systems in environments with untrusted wireless networks

Patch Information

Multiple patches have been released to address this vulnerability. The fix ensures NUL termination is enforced before the iwl_fw_ini_debug_info_tlv string is used. Apply the appropriate patch for your kernel version:

• Kernel Patch Commit 71d4186
• Kernel Patch Commit 783d413
• Kernel Patch Commit 96aa407
• Kernel Patch Commit c855a1a
• Kernel Patch Commit ea1d166
• Kernel Patch Commit fabe2db
• Kernel Patch Commit fec14d1

Debian users should refer to the Debian LTS Announcement for distribution-specific guidance.

Workarounds

• Disable the iwlwifi driver by blacklisting the module if WiFi functionality is not required: add blacklist iwlwifi to /etc/modprobe.d/blacklist.conf
• Use wired Ethernet connections on critical systems until patches can be applied
• Implement network segmentation to limit exposure of vulnerable systems to untrusted wireless networks
• Consider using alternative WiFi drivers if available for your hardware

# Blacklist iwlwifi module as temporary workaround
echo "blacklist iwlwifi" | sudo tee /etc/modprobe.d/blacklist-iwlwifi.conf
sudo update-initramfs -u
sudo reboot

# Verify module is not loaded after reboot
lsmod | grep iwlwifi