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Unlock with Pro - from £29/user/moDetect Kube-logging Logging Operator Fluentd Configuration Injection RCE (CVE-2026-54680) in Splunk
Detects exploitation of CVE-2026-54680, a critical (CVSS 9.9) configuration injection vulnerability in kube-logging logging-operator (versions prior to the 0.0.0-20260608145523-cf437d7f1e05 pseudo-version / 6.6.0 release) that allows an attacker with the ability to influence Fluentd/Fluent Bit configuration inputs (e.g. via Flow/ClusterFlow/Output CRDs, log forwarding pipelines, or unsanitized log fields reflected into config templates) to inject arbitrary Fluentd configuration directives. This injection can lead to remote code execution via Fluentd's exec plugin, ruby code blocks, or file-based output writes, potentially compromising the logging-operator pod and any Kubernetes service account/token it holds, enabling lateral movement and cluster compromise.
MITRE ATT&CK
SPL Detection Query
index=kubernetes sourcetype IN ("kube:audit", "fluentd:log", "fluent-bit:log")
(kind="Flow" OR kind="ClusterFlow" OR kind="Output" OR kind="ClusterOutput" OR kind="Logging")
(verb="create" OR verb="update" OR verb="patch")
| eval config_content=coalesce(requestObject, _raw)
| regex config_content="(?i)(exec_filter|<exec>|<script>|ruby\s+do|system\(|`.*`|\|\s*(sh|bash)\b|/bin/(sh|bash))"
| rex field=objectRef.namespace "(?<namespace>.*)"
| table _time, sourcetype, namespace, objectRef.name, kind, verb, user.username, config_content
| append [
search index=kubernetes sourcetype="fluentd:log" (pod_name="*logging-operator*" OR pod_name="*fluentd*" OR pod_name="*fluent-bit*")
("invalid configuration" OR "parse error" OR "unexpected token" OR "exec_filter" OR "ruby eval")
| table _time, sourcetype, pod_name, namespace, _raw
]
| sort -_timeSearches Splunk-indexed Kubernetes audit and Fluentd/Fluent Bit logs for injected Fluentd configuration directives (exec, script, ruby blocks, shell command chaining) applied through logging-operator managed CRDs, consistent with exploitation of CVE-2026-54680.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Authorized DevOps pipelines that legitimately deploy exec-based output plugins
- Load testing or config validation jobs that intentionally trigger parse errors
- Verbose debug logging from fluentd that includes shell-like example text
- Scheduled configuration audits by internal compliance scanners
Other platforms for CVE-2026-54680
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.
- Test 1Inject exec directive via ClusterFlow CRD
Expected signal: Kubernetes audit log entries for create operations on ClusterFlow and ClusterOutput resources containing an 'exec' block, followed by fluentd operator reconciliation logs regenerating the rendered configuration.
- Test 2Inject ruby eval block into Output configuration
Expected signal: Audit log capturing the Output resource creation with enableRuby=true and a system() call embedded in the record template; fluentd pod logs showing plugin reconfiguration.
- Test 3Simulate command execution artifact from compromised fluentd pod
Expected signal: Container runtime/EDR process execution events for /bin/sh, id, whoami, and cat commands executed inside the fluentd pod, plus Kubernetes audit log entry for the 'pods/exec' subresource.
References (4)
- https://github.com/kube-logging/logging-operator/security/advisories/GHSA-mjqf-28ph-426h
- https://github.com/kube-logging/logging-operator/commit/cf437d7f1e056c78740bf5716ac8bdebcf002425
- https://github.com/kube-logging/logging-operator/releases/tag/6.6.0
- https://github.com/advisories/GHSA-mjqf-28ph-426h
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