CVE-2026-47336: AppArmor Socket Mediation Bypass in Ubuntu Linux 6.8

Technical summary

CVE-2026-47336 is rooted in CWE-457 (Use of Uninitialized Variable) within Ubuntu Linux 6.8's AppArmor kernel module. Specifically, the AF_INET and AF_INET6 socket mediation code contains an uninitialized variable that affects security policy evaluation. When an unprivileged local user triggers socket-related operations, the uninitialized variable can cause AppArmor's access control decision to be incorrect or inconsistent. This results in improper mediation of network socket permissions, allowing operations that should be denied under a restrictive AppArmor profile to proceed. The CVSS 3.1 vector (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N) reflects low attack complexity, local-only attack surface, low privilege requirement, and integrity impact without confidentiality or availability consequences.

Business impact

Organizations relying on AppArmor for mandatory access control (MAC) enforcement face a potential weakening of their security posture. If applications or services are confined via AppArmor profiles that restrict network socket access, a local user could circumvent those restrictions to establish unauthorized network connections. In multi-tenant or container-based environments where AppArmor provides isolation boundaries between workloads, this could enable lateral movement or unauthorized inter-process communication. The integrity impact is classified as low because the vulnerability does not directly lead to privilege escalation, data exfiltration, or system unavailability—but it does create a compliance and control gap where expected restrictions become unreliable.

Affected systems

Only Ubuntu Linux 6.8 is affected. Organizations running other Ubuntu LTS or non-LTS versions, or non-Ubuntu distributions, are not impacted by this specific vulnerability. If you use Ubuntu 6.8 with AppArmor enabled (which is typical in modern Ubuntu deployments), and if you have AppArmor profiles that restrict socket access for any processes, this vulnerability could affect enforcement.

Exploitability

This vulnerability is not currently listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, indicating no public evidence of active exploitation in the wild. Exploitation requires local user access and unprivileged context; remote exploitation is not possible. An attacker would need to already have a shell or login session on the target system. The bug is triggered through normal socket operations, with no special exploit code or complex trigger mechanism required—a determined local user could discover the weakened policy enforcement through straightforward testing. The low CVSS score reflects the requirement for pre-existing local access.

Remediation

Apply the security update provided by Canonical for Ubuntu Linux 6.8, which patches the uninitialized variable in AppArmor's socket mediation code. Verify that the update is applied via standard Ubuntu package management channels and that the system is rebooted if required. Organizations should also review their AppArmor profiles to confirm they are correctly restricting socket access as intended, and conduct testing post-patch to validate that access controls are now enforced as expected.

Patch guidance

Ubuntu will release a kernel security update to address this issue. Check Canonical's security advisories and apply the patch through 'apt update' and 'apt upgrade' or your Ubuntu patch management system. Verify the patch has been applied by confirming the kernel version has been updated. A reboot may be required; plan maintenance windows accordingly. Ensure your AppArmor policies are re-validated after the patch to confirm correct enforcement.

Detection guidance

Monitor system logs for AppArmor denials and audit logs to detect anomalies in socket creation or binding by unprivileged users that should have been restricted by AppArmor profiles. Use 'aa-logprof' or similar AppArmor analysis tools to review policy violations. If you have AppArmor running in 'enforce' mode, you should not see unexpected socket operations succeed—if they do after this CVE is disclosed, investigate whether your system is patched. Conduct periodic review of AppArmor profile effectiveness with tools like 'aa-status' to ensure policies remain consistent and active.

Why prioritize this

Despite the low CVSS score, this vulnerability merits prompt but not emergency remediation. It directly weakens a core security control (AppArmor MAC) in environments that depend on it for workload isolation or privilege boundary enforcement. Organizations using AppArmor should prioritize patching within their normal security update cycle. Those using AppArmor in high-security or multi-tenant deployments should consider patching sooner. The lack of KEV listing and low severity score means this does not require immediate weekend patching, but should not be deferred indefinitely.

Risk score, explained

The CVSS 3.1 score of 3.3 (LOW) reflects the combination of local-only attack vector, low privilege requirement, and low complexity, offset by a tangible but limited integrity impact. No confidentiality or availability impact occurs directly. The score does not account for the architectural importance of AppArmor in modern Linux security, which may justify higher organizational priority despite the numerical rating. This is a reminder that CVSS is a technical baseline, not a business prioritization tool.

Frequently asked questions