Detect Nuclio Cron Trigger Header/Body Command Injection (CVE-2026-52831) in Splunk
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
SPL Detection Query
index=kubernetes sourcetype="kube:container:log" (namespace="nuclio" OR container_name="*nuclio*" OR container_name="*processor*")
| regex log="(;|\||&&|\$\(|`|>|<|\bcurl\b|\bwget\b|\bnc\b|/bin/sh|/bin/bash)"
| eval injection_indicator=1
| table _time, namespace, pod_name, container_name, log
| sort -_timeIdentifies suspicious shell metacharacters or exploitation utility invocations within Nuclio processor container logs, consistent with cron trigger header/body injection exploitation of CVE-2026-52831.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Functions that intentionally invoke shell utilities as part of normal operation
- Verbose debug logs echoing raw request data
- Third-party monitoring agents injecting metacharacters into log lines
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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