CVE-2024-41091: Linux Kernel Buffer Overflow Vulnerability

CVE-2024-41091 Overview

CVE-2024-41091 is an Out-of-Bounds Read vulnerability in the Linux kernel's TUN (network tunnel) driver. The vulnerability exists in the tun_xdp_one() code path where a missing frame length validation check allows corrupted socket buffers (skb) to be processed and sent downstream. This flaw enables a local attacker with low privileges to potentially read sensitive kernel memory or cause system instability.

The vulnerability occurs because the tun_xdp_one() function fails to verify that incoming frames meet the minimum Ethernet header size (ETH_HLEN) before processing. When a short frame is received, the eth_type_trans() function may attempt to access memory beyond the actual frame boundaries, leading to out-of-bounds memory access.

Critical Impact

Local attackers can exploit this vulnerability to read sensitive kernel memory or cause denial of service conditions on affected Linux systems through malformed network frames in the TUN/TAP driver.

Affected Products

• Linux Kernel (multiple versions with TUN/TAP driver support)
• Linux-based systems using virtual network interfaces (VMs, containers)
• Network virtualization platforms utilizing TUN devices

Discovery Timeline

• July 29, 2024 - CVE-2024-41091 published to NVD
• November 3, 2025 - Last updated in NVD database

Technical Details for CVE-2024-41091

Vulnerability Analysis

The Linux kernel TUN driver provides virtual network device functionality, commonly used in VPN applications, container networking, and virtual machine environments. The vulnerability stems from an incomplete security check in the XDP (eXpress Data Path) processing code path.

When network frames are processed through the tun_xdp_one() function, the code fails to validate that the frame length meets the minimum Ethernet header requirement of 14 bytes (ETH_HLEN). This oversight allows malformed short frames to pass through validation and be processed by eth_type_trans(), which assumes a valid Ethernet header is present.

The alternative processing path through tun_get_user() correctly implements this validation for IFF_TAP interfaces, prohibiting frames shorter than the Ethernet header size. This inconsistency between code paths created a security gap that attackers could exploit through the XDP pathway.

Root Cause

The root cause is a missing boundary check in the tun_xdp_one() function. While the tun_get_user() function properly validates frame lengths against ETH_HLEN before processing, this critical validation was omitted from the XDP code path. This CWE-125 (Out-of-Bounds Read) vulnerability allows the kernel to read memory beyond allocated frame buffers when processing maliciously crafted short frames.

Attack Vector

The attack requires local access to the system with low privileges. An attacker must be able to interact with TUN/TAP devices, which is common in containerized environments or systems with network virtualization. The attacker can:

1. Open or access a TUN/TAP device on the target system
2. Send specially crafted network frames shorter than the Ethernet header size (less than 14 bytes)
3. These malformed frames bypass length validation in tun_xdp_one()
4. The eth_type_trans() function attempts to read the Ethernet header, accessing memory beyond the frame's actual boundaries
5. This results in out-of-bounds read operations that may leak kernel memory or cause system instability

The fix implements the same frame length validation in tun_xdp_one() that already exists in tun_get_user(), ensuring all frames shorter than the Ethernet header size are dropped before processing.

Detection Methods for CVE-2024-41091

Indicators of Compromise

• Unexpected kernel crashes or panics related to the TUN driver or network subsystem
• Kernel log messages indicating memory access violations in the tun module
• Unusual network activity on TUN/TAP interfaces with malformed or undersized frames
• System instability when running containerized workloads or VPN applications

Detection Strategies

• Monitor kernel logs (dmesg) for out-of-bounds access warnings related to the tun module
• Implement kernel runtime protection tools that detect anomalous memory access patterns
• Use SentinelOne's kernel-level monitoring to detect exploitation attempts targeting the TUN driver
• Deploy network monitoring to identify abnormal frame sizes on virtual network interfaces

Monitoring Recommendations

• Enable kernel auditing for TUN/TAP device operations and access patterns
• Configure SentinelOne endpoint agents to monitor for kernel vulnerability exploitation attempts
• Implement system call monitoring for ioctl operations on /dev/net/tun devices
• Review container and VM network configurations for exposed TUN/TAP interfaces

How to Mitigate CVE-2024-41091

Immediate Actions Required

• Update the Linux kernel to a patched version that includes the frame length validation fix
• Restrict access to TUN/TAP devices using proper file permissions and user group controls
• Review and limit which applications and users can create or access virtual network interfaces
• Apply vendor-specific security updates from your Linux distribution

Patch Information

Multiple kernel patches have been released to address this vulnerability. The fix adds a frame length check in tun_xdp_one() to drop frames shorter than the Ethernet header size, consistent with the existing validation in tun_get_user(). Apply the appropriate patch for your kernel version:

• Linux Kernel Commit 0495848
• Linux Kernel Commit 32b0aab
• Linux Kernel Commit 589382f
• Linux Kernel Commit 6100e02
• Linux Kernel Commit 8418f55
• Linux Kernel Commit a9d1c27
• Linux Kernel Commit ad6b3f6
• Linux Kernel Commit d5ad89b

Debian users should also review the Debian LTS Security Announcement for distribution-specific updates.

Workarounds

• Restrict access to /dev/net/tun by modifying device permissions to limit which users can interact with TUN/TAP devices
• Disable unused TUN/TAP functionality by unloading the tun kernel module if virtual networking is not required: modprobe -r tun
• Implement network namespaces with restricted capabilities to isolate processes that require TUN/TAP access
• Use container security policies to prevent untrusted workloads from accessing TUN devices

# Restrict TUN device access to root and specific groups
chmod 0660 /dev/net/tun
chown root:netdev /dev/net/tun

# Disable TUN module if not needed
echo "blacklist tun" >> /etc/modprobe.d/blacklist-tun.conf
modprobe -r tun