CVE-2026-68336: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-68336 Overview

CVE-2026-68336 is a NULL pointer dereference vulnerability in the Linux kernel's bonding driver. The flaw occurs when the kernel is booted with the ipv6.disable=1 parameter. Under that configuration, inet6_init() exits before addrconf_init() runs, leaving net->ipv6.devconf_all uninitialized. The bonding driver's bond_send_validate() still calls bond_ns_send_all(), which routes into ip6_pol_route() and dereferences the NULL devconf_all pointer. The result is a kernel oops in the bond_arp_monitor workqueue path, causing a denial of service on affected systems that use link bonding with IPv6 disabled.

Critical Impact
A kernel NULL pointer dereference in the bonding driver can crash the kernel on systems booted with ipv6.disable=1, breaking network availability on bonded interfaces.

Affected Products

Linux kernel bonding driver
Systems booted with the ipv6.disable=1 kernel parameter
Configurations using active-backup ARP monitoring with bonded interfaces

Discovery Timeline

2026-08-10 - CVE-2026-68336 published to NVD
2026-08-10 - Last updated in NVD database

Technical Details for CVE-2026-68336

Vulnerability Analysis

The vulnerability is a [CWE-476] NULL pointer dereference triggered from the bonding driver's ARP monitor worker. When Linux boots with ipv6.disable=1, the IPv6 subsystem short-circuits initialization: inet6_init() returns early and addrconf_init() never executes. That leaves the per-namespace net->ipv6.devconf_all pointer uninitialized.

Despite IPv6 being disabled, bond_send_validate() unconditionally calls bond_ns_send_all() to send IPv6 Neighbor Solicitation probes for slave validation. The call chain proceeds through ip6_route_output_flags() into fib6_rule_lookup() and ip6_pol_route(), where net->ipv6.devconf_all is dereferenced. The reported crash address 0x0c reflects an offset access on a NULL base.

The upstream fix adds an ipv6_mod_enabled() guard in the caller so that IPv6 neighbor solicitation is skipped entirely when the IPv6 module is disabled. See Kernel Commit 992dce02bda for the mainline fix and the additional stable backports.

Root Cause

The bonding driver assumes that the IPv6 stack is initialized whenever the kernel is built with IPv6 support. bond_ns_send_all() does not check whether the IPv6 module was disabled at runtime via the ipv6.disable=1 boot parameter. The kernel therefore issues an IPv6 route lookup against a namespace whose devconf_all field was never allocated.

Attack Vector

Exploitation requires the local system to be configured with a bonded interface using ARP-based monitoring and booted with ipv6.disable=1. The crash triggers from the kernel's own bond_arp_monitor workqueue during normal slave validation. There is no known remote or unauthenticated network attack vector. The primary security impact is availability: an unprivileged workqueue callback panics the kernel or renders bonded networking unusable.

The vulnerability manifests entirely within kernel context, so no exploitation code is applicable. Refer to the referenced stable-tree commits for the full source-level patch.

Detection Methods for CVE-2026-68336

Indicators of Compromise

Kernel oops messages referencing ip6_pol_route+0x69 with a fault address near 0x0c.
Stack traces from the bond_arp_monitor workqueue containing bond_ns_send_all and bond_ab_arp_probe.
Kernel logs showing BUG: kernel NULL pointer dereference on hosts booted with ipv6.disable=1.

Detection Strategies

Inventory Linux hosts whose kernel command line includes ipv6.disable=1 and that also load the bonding module.
Correlate dmesg and journalctl -k output for crash signatures involving bond_ns_send_all and ip6_pol_route.
Track running kernel versions against the fixed commits published on git.kernel.org to identify unpatched systems.

Monitoring Recommendations

Forward kernel logs to a centralized logging pipeline and alert on NULL pointer dereference events from the bonding driver.
Monitor bonded interface health, ARP monitor state, and unexpected node reboots as availability indicators.
Track kernel package versions across the fleet and flag hosts that have not received the stable backport.

How to Mitigate CVE-2026-68336

Immediate Actions Required

Apply the distribution kernel update that incorporates the upstream bonding fix referenced by the kernel.org stable commits.
On hosts that cannot be patched immediately, remove the ipv6.disable=1 boot parameter so devconf_all is initialized.
Audit bonding configurations that rely on ARP monitoring to confirm they run on patched kernels before returning to production.

Patch Information

The upstream fix adds an ipv6_mod_enabled() check in the caller of bond_ns_send_all() so that IPv6 neighbor solicitation is skipped when IPv6 is disabled. Patches are available in the stable tree via Kernel Commit 1c975de3343, Kernel Commit 2a4bad24ac5, Kernel Commit 690ce667827, Kernel Commit 738039ad21e, and Kernel Commit 992dce02bda.

Workarounds

Re-enable IPv6 at boot by removing ipv6.disable=1 from the kernel command line and disable IPv6 through sysctl instead if required by policy.
Switch bonded interfaces from ARP monitoring to MII link monitoring, which does not invoke the IPv6 route lookup path.
Unload or avoid loading the bonding module on hosts that must boot with ipv6.disable=1 until a patched kernel is installed.

bash

# Verify current kernel command line and bonding configuration
cat /proc/cmdline
modinfo bonding | grep -E '^(filename|version)'

# Example: disable IPv6 via sysctl instead of ipv6.disable=1
echo 'net.ipv6.conf.all.disable_ipv6 = 1' | sudo tee /etc/sysctl.d/99-disable-ipv6.conf
echo 'net.ipv6.conf.default.disable_ipv6 = 1' | sudo tee -a /etc/sysctl.d/99-disable-ipv6.conf
sudo sysctl --system

# Example: switch bond0 from ARP monitoring to MII monitoring
sudo ip link set bond0 down
echo 0 | sudo tee /sys/class/net/bond0/bonding/arp_interval
echo 100 | sudo tee /sys/class/net/bond0/bonding/miimon
sudo ip link set bond0 up