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[New Rule] Forbidden Request from Unusual User Agent in Kubernetes #4818

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Merged
merged 3 commits into from
Jun 19, 2025
Merged

[New Rule] Forbidden Request from Unusual User Agent in Kubernetes #4818

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[New Rule] Forbidden Request from Unusual User Agent in Kubernetes
Aegrah Jun 17, 2025
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Update rules/integrations/kubernetes/execution_forbidden_request_from…
Aegrah Jun 18, 2025
c9c8d68
Merge branch 'main' into new-rule-uncommon-user-agent-exec
Aegrah Jun 19, 2025
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42 changes: 42 additions & 0 deletions rules/integrations/kubernetes/execution_forbidden_request_from_unsual_user_agent.toml
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[metadata]
creation_date = "2025/06/17"
integration = ["kubernetes"]
maturity = "production"
updated_date = "2025/06/17"

[rule]
author = ["Elastic"]
description = """
This rule detects when a forbidden request is made from an unusual user agent in a Kubernetes environment.
Adversary tooling may use non-standard or unexpected user agents to interact with the Kubernetes API, which
can indicate an attempt to evade detection or blend in with legitimate traffic. In combination with a forbidden
request, this behavior can suggest an adversary is attempting to exploit vulnerabilities or misconfigurations
in the Kubernetes cluster.
"""
index = ["logs-kubernetes.audit_logs-*"]
language = "eql"
license = "Elastic License v2"
name = "Forbidden Request from Unusual User Agent in Kubernetes"
risk_score = 47
rule_id = "4b77d382-b78e-4aae-85a0-8841b80e4fc4"
severity = "medium"
tags = ["Data Source: Kubernetes", "Tactic: Execution"]
timestamp_override = "event.ingested"
type = "eql"
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If not sequencing and identifying rare user agents, should we consider New Terms for this rule on user agent?
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I was considering this, but now that we know that new_terms is relatively expensive in terms of compute, I wanted to go the EQL route, using currently available telemetry to tune out any non-usual ones over the last 90d.

In case this one were to remain noisy, I will move to new_terms.
query = '''
any where host.os.type == "linux" and event.dataset == "kubernetes.audit_logs" and
kubernetes.audit.stage == "ResponseComplete" and `kubernetes.audit.annotations.authorization_k8s_io/decision` == "forbid" and
not user_agent.original like~ (
"/", "karpenter", "csi-secrets-store/*", "elastic-agent/*", "agentbeat/*", "insights-operator*", "oc/*", "cloud-defend/*",
"OpenAPI-Generator/*", "local-storage-operator/*", "falcon-client/*", "nginx-ingress-controller/*", "config-translator/*",
"kwatch/*", "PrometheusOperator/*", "kube*"
)
'''

[[rule.threat]]
framework = "MITRE ATT&CK"

[rule.threat.tactic]
id = "TA0002"
name = "Execution"
reference = "https://attack.mitre.org/tactics/TA0002/"
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