Detect Nuclio Cron Trigger Header/Body Command Injection (CVE-2026-52831) in Elastic Security
Detects exploitation of CVE-2026-52831, a critical (CVSS 10.0) command injection vulnerability in Nuclio's cron trigger handling. Unsanitized event headers and body content are injected into a CronJob-generated shell command, enabling unauthenticated attackers to achieve persistent remote code execution inside Nuclio function containers and, from there, the underlying Kubernetes node. Detection focuses on shell metacharacter injection in Nuclio dashboard/trigger logs, anomalous child processes spawned from nuclio-handler/processor binaries, and suspicious CronJob-launched shell activity in Kubernetes.
MITRE ATT&CK
Elastic Detection Query
process where event.type == "start" and
process.parent.name in ("nuclio-handler", "processor", "handler") and
(process.name in ("sh", "bash", "dash") or
process.args : ("curl*", "wget*", "nc*", "*|*", "*;*", "*&&*", "*$(*"))Detects anomalous shell process execution spawned as a child of Nuclio processor/handler processes, consistent with command injection via cron trigger event data exploiting CVE-2026-52831.
Data Sources
Required Tables
False Positives & Tuning
- Custom Nuclio functions designed to invoke shell scripts as part of legitimate business logic
- Init containers or sidecars that legitimately spawn shell subprocesses
- Function runtime wrappers that use sh -c for environment setup
Other platforms for CVE-2026-52831
Testing Methodology
Validate this detection against 4 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.
- Test 1Simulate malicious cron trigger header injection
Expected signal: Nuclio processor container log entries showing the injected header value and a subsequent shell process (sh/bash) spawned as a child of the processor binary
- Test 2Simulate cron trigger body command injection
Expected signal: Outbound HTTP request from the Nuclio processor container to attacker.lab.local and creation of a curl child process under the processor binary
- Test 3Detect unpatched Nuclio dashboard version
Expected signal: Nuclio dashboard API access log entry for /api/versions endpoint request
- Test 4Simulate persistent CronJob creation via injection
Expected signal: Kubernetes audit log CronJob create event in the nuclio namespace originating from an in-cluster service account associated with the processor pod
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