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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-56743: 0.25% estimated exploitation activity in the next 30 days; percentile 16.20 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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: 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…

Published by the source

3 Sep 2026, 17:17 UTC

Last modified by the source

10 Sep 2026, 15:25 UTC

Source last checked

26 Oct 2026, 15:29 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-fm8w-2m5w-9j7r

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GO-2026-6367

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-fm8w-2m5w-9j7r

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# Patch Next advisory brief: CVE-2026-56743

Advisory: Cilium may unexpectedly allow ingress traffic from the local namespace when a Kubernetes NetworkPolicy is configured with an ipBlock match
IDs: CVE-2026-56743, GHSA-fm8w-2m5w-9j7r
Record: https://patchnext.com/advisories/cve-2026-56743 (revision 3, source checked 26 Oct 2026, 15:29 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/cilium/cilium 1.19.5. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/cilium/cilium: affected >= 1.19.0, < 1.19.5; fixed in 1.19.5

## Suggested inspection (read-only)
- Go github.com/cilium/cilium: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/cilium/cilium.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-fm8w-2m5w-9j7r (OSV record GHSA-fm8w-2m5w-9j7r lists affected ranges: Go github.com/cilium/cilium >=1.19.0 <1.19.5 (fixed))
- Verified: https://osv.dev/vulnerability/GO-2026-6367 (OSV record GO-2026-6367 lists affected ranges: Go github.com/cilium/cilium >=1.19.0 <1.19.5 (fixed))
- Verified: https://github.com/advisories/GHSA-fm8w-2m5w-9j7r (GitHub-reviewed advisory GHSA-fm8w-2m5w-9j7r lists affected ranges: Go github.com/cilium/cilium >=1.19.0 <1.19.5)

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