Cilium may unexpectedly allow ingress traffic from the local namespace when a Kubernetes NetworkPolicy is configured with an ipBlock match

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Cilium is a networking, observability, and security solution. From 1.19.0 to 1.19.4, standard Kubernetes NetworkPolicy specifications using CIDR-based ipBlock rules without pod or namespace selectors erroneously generate a wildcard namespace allow rule when Cilium is configured with a custom clusterName rather than the default any value. The parser incorrectly instantiates a pod selector on selectorless peer definitions, allowing traffic from other workloads in the same namespace as the subject of the policy. This issue is fixed in version 1.19.5.

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15 Jul 2026 19:15:30 UTC

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16 Jul 2026 13:03:36 UTC

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23 Oct 2026 15:48:27 UTC

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CVSS 3.1 · 5.4 CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N

Cilium is a networking, observability, and security solution. From 1.19.0 to 1.19.4, standard Kubernetes NetworkPolicy specifications using CIDR-based ipBlock rules without pod or namespace selectors erroneously generate a wildcard namespace allow rule when Cilium is configured with a custom clusterName rather than the default any value. The parser incorrectly instantiates a pod selector on selectorless peer definitions, allowing traffic from other workloads in the same namespace as the subject of the policy. This issue is fixed in version 1.19.5.

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Jul 15, 2026, 7:15:30 PM (timezone not stated)

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Jul 16, 2026, 1:03:36 PM (timezone not stated)

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15 Nov 2026 15:53:53 UTC

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EUVD CVSS 3.1 · 5.4 CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N

Cilium is a networking, observability, and security solution. From 1.19.0 to 1.19.4, standard Kubernetes NetworkPolicy specifications using CIDR-based ipBlock rules without pod or namespace selectors erroneously generate a wildcard namespace allow rule when Cilium is configured with a custom clusterName rather than the default any value. The parser incorrectly instantiates a pod selector on selectorless peer definitions, allowing traffic from other workloads in the same namespace as the subject of the policy. This issue is fixed in version 1.19.5.

Source published

15 Jul 2026 20:17:51 UTC

Source modified

17 Jul 2026 17:29:02 UTC

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25 Oct 2026 14:19:10 UTC

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CVSS 3.1 · [email protected] · Secondary · 5.4 CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N

### Impact Standard Kubernetes `NetworkPolicy` specifications using CIDR-based `ipBlock` rules without pod or namespace selectors erroneously generate a wildcard namespace allow rule under specific cluster configurations. When Cilium deployment is configured with a specific custom `clusterName` (rather than the default `"any"` value), the parser incorrectly instantiates a pod selector on selectorless peer definitions. This leads to Cilium appending an unintended wildcard namespace label selector to the policy's allowed Layer 3 rules, which allows traffic from other workloads in the same namespace as the subject of the policy. Example policy affected by this issue: ``` apiVersion: networking.k8s.io/v1 kind: NetworkPolicy metadata: name: test-server namespace: default spec: podSelector: matchLabels: app: test-server policyTypes: - Ingress ingress: - from: - ipBlock: cidr: 192.0.2.3 ``` In affected versions, this policy erroneously allows the `test-server` Pod in the `default` namespace to receive any traffic from other workloads running in the `default` namespace. ### Patches This issue has been patched in: - Cilium v1.19.5 Releases below v1.19.0 are not affected. ### This issue affects: - Cilium v1.19 between v1.19.0 and v1.19.4 inclusive ### Workarounds Developers can create the equivalent policy using CiliumNetworkPolicy [fromCIDR expressions](https://docs.cilium.io/en/stable/security/policy/layer3/#ip-cidr-based). CiliumNetworkPolicy and CiliumClusterwideNetworkPolicy are not affected by this issue. ### Acknowledgements Special thanks to @TheBeeZee for reporting this issue and preparing the fix, and to @fristonio and @odinuge for their assistance in reviewing the solution. ### For more information If a vulnerability affecting Cilium appears to have been found, the Cilium security team strongly encourages reporting it to the security mailing list at [email protected]. This is a private mailing list for the Cilium security team, and the report will be treated as top priority.

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3 Sep 2026 17:17:47 UTC

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10 Sep 2026 15:25:32 UTC

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24 Oct 2026 13:19:41 UTC

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CVSS_V3 · CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N

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Cilium may unexpectedly allow ingress traffic from the local namespace when a Kubernetes NetworkPolicy is configured with an ipBlock match in github.com/cilium/cilium

Source published

10 Sep 2026 14:48:42 UTC

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10 Sep 2026 15:25:32 UTC

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24 Oct 2026 13:19:41 UTC

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