CVE-2026-31502: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-31502 Overview

A type confusion vulnerability has been identified in the Linux kernel's team network driver that affects non-Ethernet port configurations. The vulnerability occurs when team_setup_by_port() copies port_dev->header_ops directly for non-Ethernet ports. When the team device subsequently calls dev_hard_header() or dev_parse_header(), these callbacks execute with the team net_device instead of the actual lower device, causing netdev_priv(dev) to be interpreted as an incorrect private type.

This flaw can result in a system crash due to the type confusion when stacked network topologies (such as gre -> bond -> team) invoke inherited header operations with the wrong device context.

Critical Impact

Kernel crashes and system instability in Linux environments using team network driver with non-Ethernet ports in stacked network topologies.

Affected Products

• Linux Kernel (team network driver)
• Systems using stacked network topologies with team, bonding, and GRE interfaces
• Non-Ethernet port configurations using the team driver

Discovery Timeline

• 2026-04-22 - CVE CVE-2026-31502 published to NVD
• 2026-04-23 - Last updated in NVD database

Technical Details for CVE-2026-31502

Vulnerability Analysis

This type confusion vulnerability exists within the Linux kernel's team network driver subsystem. The root issue stems from improper handling of header_ops when non-Ethernet network devices are added as ports to a team interface.

When a team device is configured with non-Ethernet lower devices, the team_setup_by_port() function directly copies the port_dev->header_ops structure from the underlying port device. The problem manifests when the team device later invokes dev_hard_header() or dev_parse_header() functions—these callbacks receive the team net_device as their context rather than the actual lower device that owns the header_ops.

As a result, when netdev_priv(dev) is called within these header operation callbacks, the kernel interprets the team device's private data as if it were the private data structure of a different device type (such as bonding). This type confusion leads to memory corruption and kernel crashes.

The syzbot fuzzer identified a crash specifically in bond_header_create(), though the actual vulnerability resides in the team driver. The crash topology involves gre -> bond -> team stacking, where team incorrectly passes its own net_device to inherited bonding header operations.

Root Cause

The vulnerability originates from the team_setup_by_port() function's direct copying of port_dev->header_ops without implementing proper wrapper functions. This design flaw means that when header operations are invoked, they execute with the team device context instead of the lower device that originally provided the header operations. The netdev_priv() macro then returns an incorrectly typed pointer, as it extracts the private data area based on the passed device rather than the device that owns the operations.

Attack Vector

The vulnerability requires local access to configure network interfaces with specific stacked topologies. An attacker with sufficient privileges to create team interfaces with non-Ethernet ports (such as GRE tunnels or bonding devices) could trigger the type confusion by:

1. Creating a stacked network topology (e.g., GRE over bonding over team)
2. Configuring the team device with non-Ethernet port members
3. Generating network traffic that invokes the inherited header_ops callbacks
4. Causing the kernel to misinterpret the team device's private data as another device type

The vulnerability results in kernel crashes and potential denial of service. While the primary impact is system stability, type confusion vulnerabilities can sometimes be leveraged for more severe exploitation scenarios.

Detection Methods for CVE-2026-31502

Indicators of Compromise

• Kernel panic messages referencing bond_header_create() or similar header operation functions
• System crashes occurring when team interfaces are configured with non-Ethernet ports
• Kernel oops reports involving netdev_priv() type mismatches in network driver code
• Unexpected system reboots in environments using complex network stacking configurations

Detection Strategies

• Monitor kernel logs for crashes in network subsystem header operation functions
• Implement kernel crash dump analysis to identify type confusion patterns in team/bonding driver interactions
• Deploy syzbot-style fuzzing in test environments to identify vulnerable configurations
• Review network interface configurations for team devices using non-Ethernet ports

Monitoring Recommendations

• Enable kernel crash dump collection (kdump) to capture detailed crash information
• Configure syslog alerting for kernel oops and panic events related to network drivers
• Monitor for unusual network interface creation patterns involving team, bonding, and tunnel interfaces
• Implement file integrity monitoring on kernel modules in /lib/modules/

How to Mitigate CVE-2026-31502

Immediate Actions Required

• Apply the kernel patches from the stable kernel tree immediately
• Audit network configurations for team interfaces using non-Ethernet port members
• Consider temporarily avoiding team driver configurations with GRE, bonding, or other non-Ethernet lower devices
• Implement kernel live patching if available to minimize downtime

Patch Information

The Linux kernel maintainers have released patches to address this vulnerability. The fix introduces team header_ops wrapper functions for create and parse operations. These wrappers select a team port under RCU protection and invoke the lower device callbacks with the correct port->dev context, ensuring each callback receives the appropriate net_device structure.

Patches are available from the following kernel git commits:

• Kernel Git Commit 0a7468e
• Kernel Git Commit 20491d3
• Kernel Git Commit 425000d
• Kernel Git Commit 6d3161f

Workarounds

• Avoid using team interfaces with non-Ethernet port members until patches are applied
• Replace team driver configurations with alternative bonding configurations where possible
• Implement network segmentation to isolate systems running vulnerable configurations
• Use container or VM isolation for workloads requiring complex network stacking topologies

# Check for team interfaces with potentially vulnerable configurations
ip -d link show type team

# List team device ports
teamnl team0 ports

# Temporarily remove non-Ethernet ports from team devices
teamdctl team0 port remove gre0