Cilium with misconfigured toGroups in policies can lead to unrestricted egress traffic

### Impact `CiliumNetworkPolicy`s which use `egress.toGroups.aws.securityGroupsIds` to reference AWS security group IDs that do not exist or are not attached to any network interface may unintentionally allow broader outbound access than intended by the policy authors. In such cases, the toCIDRset section of the derived policy is not generated, which means outbound traffic may be permitted to more destinations than originally intended. ### Patches This issue has been patched in: * Cilium v1.18.4 * Cilium v1.17.10 * Cilium v1.16.17 ### This issue affects: - Cilium v1.18 between v1.18.0 and v1.18.3 inclusive - Cilium v1.17 between v1.17.0 and v1.17.9 inclusive - Cilium v1.16.16 and below ### Workarounds There is no workaround to this issue. ### Acknowledgements The Cilium community has worked together with members of Isovalent to prepare these mitigations. Special thanks to @SeanEmac for reporting this issue and to @fristonio for the patch. ### For more information If you think you have found a vulnerability affecting Cilium, we strongly encourage you to report it to our security mailing list at [[email protected]](mailto:[email protected]). This is a private mailing list for the Cilium security team, and your report will be treated as top priority.

Source published

1 Dec 2025 18:59:54 UTC

Source modified

10 Sep 2026 03:50:31 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

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

Publisher rating · MODERATE