CVE-2026-23103: Linux Kernel Race Condition Vulnerability

CVE-2026-23103 Overview

A race condition vulnerability has been identified in the Linux kernel's ipvlan network driver. The vulnerability exists in the address locking mechanism where the addrs_lock was implemented per ipvlan device rather than per port. This design flaw can lead to race conditions when handling IPv6 address changes, as IPv6 address events can occur without holding the rtnl_lock.

Critical Impact

Race conditions in the ipvlan driver can cause false-negative address validation checks and potential data corruption when multiple CPUs simultaneously manipulate IP addresses on ipvlan interfaces.

Affected Products

• Linux kernel with ipvlan driver enabled
• Systems using ipvlan network virtualization
• Container environments utilizing ipvlan networking mode

Discovery Timeline

• 2026-02-04 - CVE CVE-2026-23103 published to NVD
• 2026-02-05 - Last updated in NVD database

Technical Details for CVE-2026-23103

Vulnerability Analysis

The vulnerability stems from an architectural assumption in the original ipvlan implementation that all address changes would occur under the RTNL (Routing Netlink) lock. However, this assumption does not hold true for IPv6 address operations. The ipvlan_addr6_event() function can be invoked without the rtnl_lock being held, creating a window for race conditions.

When two CPUs attempt to add addresses simultaneously, the per-device locking scheme allows one interface to iterate through port->ipvlans and ipvlan->addrs under its own spinlock while another interface adds an IP address under a different lock. This can result in inconsistent state observations and potential false-negative results from ipvlan_addr_busy() validation checks.

Additionally, the ipvlan_ht_addr_add(port) function operates on port-level hash tables but was being called under different ipvlan device locks, creating another race condition vector. The fix introduces a per-port addrs_lock and corrects missing lock acquisitions in ipvlan_open() and ipvlan_close() functions.

Root Cause

The root cause is an improper synchronization design where the addrs_lock spinlock was implemented at the ipvlan device level instead of the port level. Since address operations affect port-wide data structures (including the address hash table), using device-level locks creates insufficient protection for shared resources. The IPv6 address event handler pathway that bypasses RTNL lock acquisition exposes this synchronization gap.

Attack Vector

Exploitation of this vulnerability requires local access to a system with ipvlan interfaces configured. An attacker with the ability to trigger IPv6 address assignments on multiple ipvlan interfaces simultaneously could potentially:

1. Cause ipvlan_addr_busy() to return false negatives, allowing duplicate address assignments
2. Trigger race conditions in ipvlan_ht_addr_add() leading to hash table corruption
3. Exploit timing windows during ipvlan_open() and ipvlan_close() operations

The vulnerability is considered low-severity in practice because triggering simultaneous address additions across multiple CPUs targeting the same port is highly unlikely in normal operation. However, in high-density container environments with automated network configuration, the probability increases.

Detection Methods for CVE-2026-23103

Indicators of Compromise

• Unexpected duplicate IPv6 address assignments across ipvlan interfaces sharing the same port
• Kernel warnings or oops messages related to ipvlan address handling
• Network connectivity issues on ipvlan interfaces after rapid address configuration changes
• Hash table corruption indicators in ipvlan driver diagnostics

Detection Strategies

• Monitor kernel logs for ipvlan-related warnings using dmesg | grep -i ipvlan
• Implement kernel tracepoints on ipvlan address management functions
• Deploy eBPF programs to monitor spinlock contention on ipvlan data structures
• Enable lockdep debugging in development environments to detect lock ordering violations

Monitoring Recommendations

• Configure system monitoring to alert on ipvlan driver errors and warnings
• Track IPv6 address assignment events on systems with ipvlan networking enabled
• Monitor for unusual network behavior on containerized workloads using ipvlan mode
• Review kernel crash dumps for ipvlan-related stack traces

How to Mitigate CVE-2026-23103

Immediate Actions Required

• Update the Linux kernel to a patched version containing the per-port locking fix
• Review ipvlan configurations and consider temporary migration to alternative networking modes if patches cannot be immediately applied
• Limit IPv6 address manipulation operations during the vulnerability window
• Monitor affected systems for signs of exploitation

Patch Information

The vulnerability has been resolved through multiple kernel commits that introduce per-port address locking. The patches are available in the stable kernel branches:

• Linux Kernel Commit 04ba6de
• Linux Kernel Commit 1f300c1
• Linux Kernel Commit 6a81e2d
• Linux Kernel Commit d3ba321

Apply the appropriate patch for your kernel version by updating to the latest stable release in your distribution's package repositories.

Workarounds

• Disable IPv6 on ipvlan interfaces if IPv6 functionality is not required: sysctl -w net.ipv6.conf.<interface>.disable_ipv6=1
• Use macvlan or bridge networking modes as temporary alternatives to ipvlan
• Serialize IPv6 address configuration operations through orchestration controls
• Implement network namespace isolation to reduce concurrent access to ipvlan ports

# Disable IPv6 on specific ipvlan interface as temporary workaround
sysctl -w net.ipv6.conf.ipvlan0.disable_ipv6=1

# Verify ipvlan module version and check for patches
modinfo ipvlan

# Check current kernel version for patch status
uname -r