How severe is CVE-2026-56743?

CVE-2026-56743 has a CVSS score of 5.4/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-56743?

CVE-2026-56743 affects the following packages: github.com/cilium/cilium (Go). Ecosystems affected: Go.

How do I fix CVE-2026-56743?

Update github.com/cilium/cilium to 1.19.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-56743 is resolved across your whole dependency graph.

How do I detect CVE-2026-56743 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/cilium/cilium, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-56743 if there is no patch (or I can't update yet)?

Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Is CVE-2026-56743 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-56743 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-56743?

CVE-2026-56743 has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 15th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-56743?

CVE-2026-56743 is classified as CWE-863 (CWE-863). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-56743 published, and has it been updated?

CVE-2026-56743 was published on July 15, 2026 and was last updated on September 27, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

MEDIUM severity

CVE-2026-56743 — cilium

MEDIUMFix: cilium/cilium@1c84ae3

CVE-2026-56743 is a medium-severity (CVSS 5.4) CWE-863 vulnerability in github.com/cilium/cilium. A fix is available for github.com/cilium/cilium — see the affected versions and patch details below.

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

Also known asBIT-cilium-2026-56743BIT-cilium-operator-2026-56743BIT-hubble-relay-2026-56743GHSA-fm8w-2m5w-9j7rGO-2026-6367

Published

Jul 15, 2026

Updated

Sep 27, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 17, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-56743.

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs15th percentile — riskier than 15% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-56743 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 390,807 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🐹github.com/cilium/cilium

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

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. 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.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/cilium/cilium`	≥ 1.19.0&&< 1.19.5	1.19.5`go get github.com/cilium/cilium@v1.19.5`

Affected Products

1 product · 1 configurations

Application

ciliumcilium

≥ 1.19.0 && < 1.19.5

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/cilium/cilium, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/cilium/cilium to 1.19.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-56743 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Frequently Asked Questions

### 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 name