Copy-fail-destroyer: K8s remediation for CVE-2026-31431

Source: Hacker News

copy-fail-destroyer

A Kubernetes DaemonSet agent that detects and remediates CVE-2026-31431 (“Copy Fail”) — an algif_aead in‑place logic flaw in the Linux kernel allowing unprivileged page‑cache writes via the AF_ALG socket interface.

What it does

On each node the agent runs a loop every 5 minutes that:

• Checks the kernel version against all known patched stable branches.
• Probes the AF_ALG module by attempting to create and bind an AF_ALG socket to aead / authenc(hmac(sha256),cbc(aes)) — the exact algorithm the exploit targets. This is safe and non‑destructive.
• Remediates based on the configured REMEDIATION_MODE (see below).
• Exposes Prometheus metrics so you can alert and track status across the fleet.

Remediation modes

Set via the REMEDIATION_MODE environment variable (or remediationMode in the Helm chart):

Prometheus metrics

All metrics are exposed on :9100/metrics.

Patched kernel versions

CVE-2026-31431 (Copy Fail)

• 7.0+ (mainline)
• 6.19.12+, 6.18.22+
• Kernels before 4.14 are not affected (bug introduced in 4.14).

Project structure

cmd/destroyer/main.go          # Entry point — metrics server, check loop, remediation
pkg/detector/
  cve202631431.go              # CVE-2026-31431 (Copy Fail) detection
  probe_linux.go               # AF_ALG module probe (Linux)
  probe_other.go               # Probe stub (non‑Linux)
  remediate_linux.go           # Module unload via delete_module (Linux)
  remediate_other.go           # Remediation stub (non‑Linux)
deploy/namespace.yaml          # Namespace with Pod Security Admission policy
deploy/daemonset.yaml          # Kubernetes DaemonSet manifest
Dockerfile                     # Multi‑stage build (scratch final image)

Building

Native

go build ./cmd/destroyer

Linux cross‑compile (for container image)

CGO_ENABLED=0 GOOS=linux go build -o destroyer ./cmd/destroyer

Container image

docker build -t copy-fail-destroyer .

Deployment

The agent requires a privileged security context to unload kernel modules and probe AF_ALG sockets. The root filesystem is read‑only.

Raw manifests

kubectl apply -f deploy/namespace.yaml
kubectl apply -f deploy/daemonset.yaml

Helm

helm install copy-fail-destroyer oci://ghcr.io/norskhelsenett/helm/copy-fail-destroyer \
  --namespace copy-fail-destroyer --create-namespace

Override the remediation mode:

helm install copy-fail-destroyer oci://ghcr.io/norskhelsenett/helm/copy-fail-destroyer \
  --namespace copy-fail-destroyer --create-namespace \
  --set remediationMode=disabled

ArgoCD

An Application manifest is provided at deploy/argocd-application.yaml. Edit targetRevision to pin a chart version, then apply:

kubectl apply -f deploy/argocd-application.yaml

The DaemonSet includes Prometheus scrape annotations (prometheus.io/scrape: "true", port 9100).

Prometheus Operator

If you use the Prometheus Operator, deploy the PodMonitor to have metrics scraped automatically.

Raw manifest

kubectl apply -f deploy/podmonitor.yaml

Via Helm

helm install copy-fail-destroyer oci://ghcr.io/norskhelsenett/helm/copy-fail-destroyer \
  --namespace copy-fail-destroyer --create-namespace \
  --set metrics.podMonitor.enabled=true

Alert rules (PrometheusRule) for Alertmanager are also available.

Raw manifest

kubectl apply -f deploy/prometheusrule.yaml

Via Helm with extra alert labels

helm install copy-fail-destroyer oci://ghcr.io/norskhelsenett/helm/copy-fail-destroyer \
  --namespace copy-fail-destroyer --create-namespace \
  --set metrics.prometheusRule.enabled=true \
  --set metrics.prometheusRule.extraAlertLabels.team=platform

Three alerts are defined:

CI/CD

A GitHub Actions workflow (.github/workflows/build.yaml) triggers on versioned tags (v*). It:

• Runs go test ./...
• Builds the Linux binary
• Builds and pushes a container image to ghcr.io/norskhelsenett/copy-fail-destroyer
• Packages and pushes the Helm chart to oci://ghcr.io/norskhelsenett/helm/copy-fail-destroyer

Tags are derived from the Git tag — e.g. pushing v1.2.3 produces image tags 1.2.3 and 1.2.

git tag v1.0.0
git push origin v1.0.0