CVE-2025-68340 in Linux
Summary
by MITRE • 12/23/2025
In the Linux kernel, the following vulnerability has been resolved:
team: Move team device type change at the end of team_port_add
Attempting to add a port device that is already up will expectedly fail, but not before modifying the team device header_ops.
In the case of the syzbot reproducer the gre0 device is already in state UP when it attempts to add it as a port device of team0, this fails but before that header_ops->create of team0 is changed from eth_header to ipgre_header in the call to team_dev_type_check_change.
Later when we end up in ipgre_header() struct ip_tunnel* points to nonsense as the private data of the device still holds a struct team.
Example sequence of iproute2 commands to reproduce the hang/BUG(): ip link add dev team0 type team ip link add dev gre0 type gre ip link set dev gre0 up ip link set dev gre0 master team0 ip link set dev team0 up ping -I team0 1.1.1.1
Move team_dev_type_check_change down where all other checks have passed as it changes the dev type with no way to restore it in case one of the checks that follow it fail.
Also make sure to preserve the origial mtu assignment: - If port_dev is not the same type as dev, dev takes mtu from port_dev - If port_dev is the same type as dev, port_dev takes mtu from dev
This is done by adding a conditional before the call to dev_set_mtu to prevent it from assigning port_dev->mtu = dev->mtu and instead letting team_dev_type_check_change assign dev->mtu = port_dev->mtu. The conditional is needed because the patch moves the call to team_dev_type_check_change past dev_set_mtu.
Testing: - team device driver in-tree selftests - Add/remove various devices as slaves of team device - syzbot
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Analysis
by VulDB Data Team • 02/26/2026
The vulnerability described in CVE-2025-68340 resides within the Linux kernel's team driver implementation, specifically concerning the handling of device type changes during port addition operations. This issue manifests when attempting to add a port device that is already in the up state to a team device, creating a scenario where the system's internal state becomes inconsistent and potentially leads to system hangs or undefined behavior. The root cause lies in the improper ordering of operations within the team_port_add function, where the team_dev_type_check_change function is invoked too early in the process, before all validation checks have completed successfully.
The technical flaw occurs due to the sequence of operations in the team_port_add function where the header_ops structure is modified before all validation checks have passed. When a port device like gre0 is already up and being added to team0, the system attempts to change the team device's header operations from eth_header to ipgre_header through team_dev_type_check_change. This premature modification causes the system to lose track of the correct device type information, leading to corruption of device private data structures. The ipgre_header function then attempts to operate on a struct ip_tunnel pointer that contains invalid data because the private data still references the original struct team structure instead of the expected tunnel structure, creating a dangerous state where memory access patterns become unpredictable.
This vulnerability has significant operational impact as it can lead to system hangs, kernel panics, or data corruption during network device management operations. The specific sequence of commands provided in the description demonstrates how an attacker or tester could trigger this condition using standard iproute2 utilities, making it particularly concerning for production systems where network reliability is critical. The issue affects systems running Linux kernels with team device drivers, potentially impacting network infrastructure, virtualization environments, and any system relying on team bonding for network redundancy or load balancing. The problem becomes more severe when considering that the system's behavior becomes unpredictable after the header operation change, making it difficult to diagnose or recover from the corrupted state.
The mitigation strategy implemented in the fix involves reordering the operations within the team_port_add function to ensure that team_dev_type_check_change is called only after all validation checks have passed successfully. This prevents the premature modification of device type information that leads to the corrupted state. Additionally, the fix addresses the MTU assignment logic by introducing a conditional check before calling dev_set_mtu, ensuring that the correct MTU values are preserved during the port addition process. The conditional prevents port_dev->mtu from being assigned dev->mtu when the port device type differs from the team device, allowing the team_dev_type_check_change function to properly assign dev->mtu = port_dev->mtu instead. This approach aligns with security best practices for state management and ensures that device type changes are atomic and reversible, preventing partial state modifications that could lead to system instability.
The vulnerability demonstrates characteristics consistent with CWE-691, which deals with insufficient control flow management, and relates to ATT&CK technique T1068, involving the exploitation of privilege escalation through kernel vulnerabilities. The fix addresses the root cause by ensuring proper control flow and state management within the kernel's network device subsystem, making it consistent with security frameworks that emphasize the importance of atomic operations and proper error handling in kernel space. Testing of this fix includes in-tree selftests for the team device driver, verification of add/remove operations with various devices, and validation through syzbot testing to ensure the fix does not introduce regressions while effectively resolving the race condition and state corruption issues.