CVE-2026-47334: Ubuntu Linux Kernel AppArmor Spinlock Denial-of-Service Vulnerability

Technical summary

CVE-2026-47334 is a kernel synchronization bug affecting Ubuntu's AppArmor SAUCE patches. The vulnerability exists in the notification handling path, where code attempts to sleep (via functions like mutex_lock or msleep) while holding a spinlock. Spinlocks are designed for brief, non-blocking critical sections; sleeping under a spinlock violates fundamental kernel synchronization semantics and leads to kernel panic or deadlock conditions. The flaw is reachable from unprivileged user-space, making it a local denial-of-service vector. The root cause is an architectural violation in the custom AppArmor patches rather than a flaw in upstream kernel code.

Business impact

This vulnerability enables any local user account to trigger unplanned kernel downtime, disrupting services on affected systems. For multi-tenant environments, container hosts, or shared systems, the impact is significant: one unprivileged user can degrade or crash the entire host. Systems requiring high availability—databases, application servers, infrastructure services—face unscheduled restarts and potential data consistency risks if transactions are interrupted. Organizations running Ubuntu 6.8, 6.17, or 7.0 should treat this as a stability and availability issue requiring prompt remediation.

Affected systems

Ubuntu Linux kernel versions 6.8, 6.17, and 7.0 are affected. This encompasses both client and server deployments, including cloud instances, virtual machines, and physical servers running these specific kernel versions. Desktop systems, development workstations, and production servers are all at risk if they run an affected kernel version. Organizations should audit kernel versions across their Ubuntu estate to identify exposure.

Exploitability

Exploitability is high for the local attack surface. No privilege escalation is needed—an unprivileged user with basic shell access can trigger the condition. No complex race conditions or multi-stage exploitation is required; the vulnerability is deterministic and easily reproducible. However, exploitation is limited to local attack vectors; remote exploitation is not possible. The barrier to triggering the bug is low, making it a practical denial-of-service tool in the hands of any local user.

Remediation

Update to a patched kernel version from Canonical. Verify the Ubuntu security advisory for the specific fixed kernel versions corresponding to your affected release. After patching, reboot to apply the new kernel. Interim mitigation could include restricting local shell access to trusted users only, though this does not eliminate the risk for legitimate users who might encounter malware or insider threats. Prioritize kernel updates on systems with broad local access or multi-tenant workloads.

Patch guidance

Consult the Ubuntu Security Notice (USN) corresponding to CVE-2026-47334 for the exact patched kernel versions and release timeline. Patches are typically available through apt; run 'apt update && apt upgrade' to pull the latest kernel package, then reboot. Verify the new kernel version using 'uname -r' post-reboot to confirm the patch was applied. Test kernel updates in a non-production environment first if feasible, though this is a stability fix with low regression risk.

Detection guidance

Monitor system logs (dmesg, /var/log/kern.log) for spinlock-related warnings or kernel panics coinciding with AppArmor activity. Watch for repeated unplanned kernel panics or system hangs without obvious cause. In containerized environments, monitor pod restarts and node health metrics for unexplained disruptions. Alerting on kernel panic events or system reboots in infrastructure monitoring tools can help identify active exploitation. Correlation with user login activity around crash times may reveal malicious local users.

Why prioritize this

This vulnerability warrants prompt but not emergency patching. With a CVSS score of 5.5 (Medium), it is lower urgency than critical remote code execution issues, yet the local denial-of-service impact on availability is material. Prioritize systems hosting multi-tenant workloads, critical infrastructure services, and high-availability platforms. Single-user development machines may be patched on a standard cycle. Organizations should complete remediation within 2–4 weeks to maintain system stability and reduce operational friction.

Risk score, explained

The CVSS 3.1 score of 5.5 reflects a localized denial-of-service with no confidentiality or integrity impact (C:N, I:N, A:H). The attack vector is local (AV:L) with low complexity (AC:L) and low privilege requirement (PR:L), indicating an unprivileged user can reliably trigger the bug. The absence of user interaction (UI:N) and system scope (S:U) confirms the issue is straightforward to exploit from within a single compromised or untrusted user context. The Medium severity reflects that availability impact is the sole concern; data leakage or corruption is not possible via this path.

Frequently asked questions