> ## Knowledge Base Index > Fetch the complete knowledge base index at: https://support.stacktrack.com/sitemap.xml > Use this file to discover available pages before exploring further. > Pure-Markdown content can be obtained by appending a '.md' suffix to the content URLs listed in the sitemap (without the trailing slash). # Kubernetes Mitigation for Copy Fail Vulnerability - CVE-2026-31431 # Kubernetes Mitigation for Copy Fail Vulnerability CVE-2026-31431 ## Purpose This document describes a Kubernetes DaemonSet used to apply a temporary mitigation for the Linux kernel Copy Fail vulnerability, tracked as CVE-2026-31431. The DaemonSet is designed to run once on every Kubernetes node and disable the vulnerable `algif_aead` kernel module by writing a modprobe rule onto the host filesystem and attempting to unload the module if it is already loaded. This is intended as a short-term mitigation only. The preferred long-term remediation is to apply the relevant vendor kernel and package updates, then reboot or roll nodes as required. ## Background Copy Fail, CVE-2026-31431, is a Linux kernel local privilege escalation vulnerability associated with the kernel cryptographic subsystem, specifically the `algif_aead` interface. A successful exploit may allow a local unprivileged user or compromised workload with sufficient local execution capability to escalate privileges on an affected Linux host. In a Kubernetes environment, the primary concern is that a compromised container, overly permissive workload, or attacker with local execution on a node could attempt to exploit the host kernel. Because Kubernetes worker nodes share the host kernel across workloads, node-level mitigation is required. ## Mitigation Summary The mitigation disables loading of the vulnerable `algif_aead` kernel module on every Kubernetes node. The DaemonSet performs the following actions: 1. Runs one privileged pod on each Kubernetes node. 2. Enters the host namespaces using `nsenter`. 3. Writes a modprobe configuration file to the host /etc/modprobe.d/disable-algif_aead.conf 4. Adds the following rule: install algif_aead /bin/false 5. Attempts to unload the module if currently loaded: rmmod algif_aead || true 6. Verifies whether the module is still loaded using `lsmod`. 7. Keeps the pod running with `sleep infinity` so that the mitigation pod remains visible on each node. ## Kubernetes DaemonSet Manifest ```html apiVersion: apps/v1 kind: DaemonSet metadata: name: copy-fail-fix namespace: kube-system spec: selector: matchLabels: name: copy-fail-fix template: metadata: labels: name: copy-fail-fix spec: hostPID: true # Required to see host processes hostNetwork: true containers: - name: fix image: alpine securityContext: privileged: true command: ["/bin/sh", "-c"] args: - | echo "Applying CVE-2026-31431 mitigation..." # Write to the host filesystem via /proc/1/root nsenter -t 1 -m -u -n -i -- \ sh -c 'echo "install algif_aead /bin/false" > /etc/modprobe.d/disable-algif_aead.conf && rmmod algif_aead || true' echo "Fix applied. Verification:" nsenter -t 1 -m -u -n -i -- lsmod | grep algif_aead || echo "Module successfully disabled." sleep infinity ``` ## Why a DaemonSet Is Used A DaemonSet is appropriate because the mitigation must be applied to every Kubernetes node, not just to a single application pod. Kubernetes workloads share the node kernel. Applying this configuration inside a normal container would only affect the container filesystem, not the host. This DaemonSet uses privileged access and namespace entry to make the change directly on the host operating system. ## Security Characteristics This DaemonSet intentionally uses elevated privileges. The following settings are required for this mitigation: | Setting | Purpose | | ---- | | `namespace: kube-system` | Runs as a cluster-level operational workload | | `hostPID: true` | Allows the pod to target host process namespace PID 1 | | `hostNetwork: true` | Allows namespace entry into the host network namespace | | `securityContext.privileged: true` | Required to enter host namespaces and modify host kernel/module configuration | | `nsenter -t 1` | Enters the host namespaces via host PID 1 | | `/proc/1/root` / host namespace access | Ensures the file is written to the node filesystem, not just the container filesystem | Because this pod is privileged, it should be treated as sensitive operational tooling. It should only be deployed by cluster administrators and should be removed once permanent patching is complete. ## Deployment Procedure ### 1. Save the manifest Save the manifest as: ``` copy-fail-fix-daemonset.yaml ``` ### 2. Apply the DaemonSet ``` kubectl apply -f copy-fail-fix-daemonset.yaml ``` ### 3. Confirm the DaemonSet is running ``` kubectl get daemonset copy-fail-fix -n kube-system ``` Expected result: ``` NAME DESIRED CURRENT READY UP-TO-DATE AVAILABLE copy-fail-fix ``` ### 4. Confirm pods are running on all expected nodes ``` kubectl get pods -n kube-system -l name=copy-fail-fix -o wide ``` Each eligible node should have one `copy-fail-fix` pod. ## Verification ### Check pod logs ``` kubectl logs -n kube-system -l name=copy-fail-fix ``` Expected log output should include: ``` Applying CVE-2026-31431 mitigation... Fix applied. Verification: Module successfully disabled. ``` If `algif_aead` still appears in the output, the module may still be loaded on that node. ### Verify directly from a node If node access is available, run: ``` lsmod | grep algif_aead ``` Expected result: ``` ``` Confirm the modprobe rule exists: ``` cat /etc/modprobe.d/disable-algif_aead.conf ``` Expected result: ``` install algif_aead /bin/false ``` ### Verify through the DaemonSet pod Select a pod: ``` kubectl get pods -n kube-system -l name=copy-fail-fix ``` Then run: ``` kubectl exec -n kube-system -- \ nsenter -t 1 -m -u -n -i -- lsmod | grep algif_aead ``` Expected result: ``` ``` ## Operational Notes * This mitigation prevents future loading of `algif_aead` using modprobe. * The DaemonSet also attempts to unload the module immediately with `rmmod`. * If the module is in use, `rmmod` may fail. The command uses `|| true` so the script continues even if unloading fails. * Nodes should still receive the official kernel or vendor security update. * A reboot or node replacement may still be required depending on the vendor patching process. * This DaemonSet does not patch the kernel; it only disables a vulnerable kernel module path. ## Risks and Considerations ### Privileged access The DaemonSet runs as a privileged workload in `kube-system`. This is powerful and should only be applied by trusted administrators. ### Compatibility Disabling `algif_aead` may affect software that relies on the Linux AF_ALG AEAD crypto interface. This is uncommon for typical Kubernetes application workloads, but it should be checked in environments with specialist cryptographic, storage, VPN, or security software. ### Persistence The modprobe configuration file is written to the node filesystem and should persist across reboot, provided the node filesystem is not ephemeral. For managed Kubernetes node groups that replace nodes from a base image, the DaemonSet should remain deployed until the underlying image or launch template includes the official fix. ### Temporary mitigation This should not be considered a substitute for kernel patching. It is a compensating control to reduce exposure until nodes are fully updated. ## Rollback Procedure Rollback should only be performed after the affected nodes have been patched or the risk has otherwise been accepted. ### 1. Remove the DaemonSet ``` kubectl delete daemonset copy-fail-fix -n kube-system ``` ### 2. Remove the modprobe configuration from each node On each node: ``` sudo rm -f /etc/modprobe.d/disable-algif_aead.conf ``` ### 3. Reload module configuration if required ``` sudo depmod -a ``` ### 4. Confirm the node has the permanent fix Verify the installed kernel/package version against vendor guidance before allowing the module to be loaded again. ## Troubleshooting ### DaemonSet pods are not created Check whether the DaemonSet exists: ``` kubectl get daemonset copy-fail-fix -n kube-system ``` Check events: ``` kubectl get events -n kube-system --sort-by=.lastTimestamp ``` ### Pods are pending Check scheduling problems: ``` kubectl describe pod -n kube-system ``` Common causes include node taints, insufficient resources, or admission policies blocking privileged pods. ### Pods fail due to Pod Security admission The DaemonSet requires privileged access. If the cluster enforces restricted Pod Security standards, the workload may be blocked. This mitigation must be deployed using an approved administrative exception or an appropriate privileged system namespace policy. ### `nsenter` is not found The manifest uses the `alpine` image. If the image does not include `nsenter` in the deployed environment, use an image that includes `util-linux`, or build a minimal internal image containing `nsenter`. Alternative images may include: * A trusted internal operations image * A hardened image containing `util-linux` * A distro image with `nsenter` installed ### Module remains loaded If logs still show `algif_aead`, the module may be in use and cannot be unloaded immediately. Actions: 1. Confirm the modprobe rule was written successfully. 2. Drain and reboot the node when operationally safe. 3. Confirm the module is not loaded after reboot. 4. Apply the official vendor patch. ## Recommended Follow-Up Actions After applying this DaemonSet: 1. Identify all affected Kubernetes node pools. 2. Apply vendor kernel and package updates. 3. Roll or reboot nodes according to the cluster maintenance process. 4. Confirm the vulnerable kernel/module path is no longer exploitable. 5. Remove the DaemonSet after permanent remediation is complete. 6. Remove the modprobe configuration only when vendor guidance confirms it is safe. 7. Record the mitigation and patch status in the incident or change record. ## Change Record Template ``` Change: Apply Kubernetes DaemonSet mitigation for Copy Fail CVE-2026-31431 Reason: Temporary mitigation for Linux kernel local privilege escalation vulnerability affecting Kubernetes worker nodes. Action taken: Deployed privileged DaemonSet copy-fail-fix in kube-system to disable algif_aead module loading and attempt module unload on each node. Validation: - DaemonSet desired/current/ready counts confirmed - Pod logs reviewed - algif_aead not present in lsmod output on target nodes - /etc/modprobe.d/disable-algif_aead.conf present on target nodes Rollback: Delete DaemonSet and remove /etc/modprobe.d/disable-algif_aead.conf from nodes after permanent vendor patching is confirmed. Owner: Date: ``` ## Status This DaemonSet provides a node-level mitigation for CVE-2026-31431 by disabling the vulnerable `algif_aead` module path. It should remain in place only until all Kubernetes nodes have received the official kernel or vendor security fix and have been rebooted or replaced as required.