CVE-2026-50563 Google Chronicle · YARA-L

Detect Fission Container Executor PodSpec Injection - Node Escape Attempt in Google Chronicle

Detects exploitation of CVE-2026-50563, a critical privilege escalation vulnerability in Fission serverless framework (<=1.23.0). The container executor allows unauthenticated or low-privileged users to inject arbitrary PodSpec fields into function pods, enabling container escape to the underlying Kubernetes node. Attackers can inject hostPID, hostNetwork, privileged containers, hostPath volume mounts, or custom service accounts to achieve full node compromise.

MITRE ATT&CK

Tactic
Privilege Escalation Lateral Movement Initial Access

YARA-L Detection Query

Google Chronicle (YARA-L)
yaral 
rule fission_podspec_injection_cve_2026_50563 {
  meta:
    author = "Detection Engineering"
    description = "Detects CVE-2026-50563 Fission PodSpec injection leading to node escape"
    severity = "CRITICAL"
    priority = "HIGH"
    reference = "https://github.com/fission/fission/security/advisories/GHSA-v455-mv2v-5g92"
    cve = "CVE-2026-50563"

  events:
    (
      $audit.metadata.event_type = "USER_RESOURCE_UPDATE_CONTENT"
      and $audit.target.namespace = /^fission/
      and $audit.target.resource.type = "pods"
      and (
        $audit.security_result.action = "ALLOW"
      )
      and (
        $audit.target.resource.attribute.labels["spec.hostPID"] = "true"
        or $audit.target.resource.attribute.labels["spec.hostNetwork"] = "true"
        or $audit.target.resource.attribute.labels["spec.hostIPC"] = "true"
        or re.regex($audit.target.resource.name, `privileged.*true|hostPath`)
      )
    )
    or
    (
      $process.metadata.event_type = "PROCESS_LAUNCH"
      and $process.target.process.file.full_path = /nsenter|unshare/
      and $process.principal.namespace = /^fission/
    )

  condition:
    $audit or $process
}
critical severity high confidence

Chronicle YARA-L rule detecting Fission namespace PodSpec injection and container escape process execution indicative of CVE-2026-50563 exploitation.

Data Sources

Google Chronicle UDM EventsKubernetes Audit Logs ingested to Chronicle

Required Tables

udm_events

False Positives & Tuning

  • Authorized cluster administration scripts that update Fission pod templates with elevated permissions for performance tuning
  • Node-level monitoring agents (e.g., Datadog, Dynatrace) that use nsenter for host metric collection within the Fission namespace
  • Fission function environment builders that temporarily require privileged access during custom runtime image construction

Other platforms for CVE-2026-50563

Microsoft Sentinel (KQL) Splunk (SPL) Elastic Security (Elastic) IBM QRadar (QRadar) Sumo Logic CSE (Sumo) CrowdStrike LogScale (LogScale) All platforms (combined) →

Testing Methodology

Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.

  1. Test 1Fission PodSpec Injection - hostPID Escape

    Expected signal: Kubernetes audit log entry with verb=create, objectRef.resource=pods, objectRef.namespace=fission-function, requestObject.spec.hostPID=true. Container process list will show host-level PIDs including kubelet, containerd, and other node processes.

  2. Test 2Fission PodSpec Injection - Privileged Container with hostPath Root Mount

    Expected signal: Kubernetes audit log with requestObject.spec.containers[0].securityContext.privileged=true and requestObject.spec.volumes containing hostPath.path=/. Container runtime logs showing privileged container start. Node-level filesystem access to /etc/passwd and hostname file.

  3. Test 3Fission Container Escape via nsenter After PodSpec Injection

    Expected signal: Process telemetry on Kubernetes node showing nsenter executed with --target 1 argument. Host PID 1 (init/systemd) namespace join event visible in node audit logs. Container log output matching host OS details rather than Alpine container OS.

Last updated: 2026-07-03 Research depth: standard
References (6)

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Tactic Hubs

TA0004Privilege EscalationTA0008Lateral MovementTA0001Initial Access

Related Techniques

T1611Escape to HostT1078Valid AccountsT1610Deploy Container

Same Tactic: Privilege Escalation

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