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PatchSiren cyber security CVE debrief

CVE-2026-56743 cilium CVE debrief

A medium-severity vulnerability was found in Cilium, a networking, observability, and security solution. The issue arises from incorrect handling of standard Kubernetes NetworkPolicy specifications using CIDR-based ipBlock rules without pod or namespace selectors when Cilium is configured with a custom clusterName. This results in the erroneous generation of a wildcard namespace allow rule, allowing traffic from other workloads in the same namespace as the subject of the policy. The vulnerability is fixed in version 1.19.5.

Vendor
cilium
Product
Unknown
CVSS
MEDIUM 5.4
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-15
Original CVE updated
2026-07-17
Advisory published
2026-07-15
Advisory updated
2026-07-17

Who should care

Users of Cilium, particularly those who have configured it with a custom clusterName and are using versions between 1.19.0 and 1.19.4, should be aware of this vulnerability and take steps to mitigate it.

Technical summary

Cilium, a networking, observability, and security solution, is vulnerable to a medium-severity issue. The problem occurs when using standard Kubernetes NetworkPolicy specifications with CIDR-based ipBlock rules lacking pod or namespace selectors, and Cilium is set up with a custom clusterName. This misconfiguration leads to the incorrect creation of a wildcard namespace allow rule, permitting traffic from other workloads within the same namespace as the policy's subject. The issue is resolved in Cilium version 1.19.5.

Defensive priority

Medium

Recommended defensive actions

  • Upgrade to Cilium version 1.19.5 or later
  • Review and update existing NetworkPolicy specifications to ensure they do not rely on CIDR-based ipBlock rules without pod or namespace selectors
  • Monitor network traffic and workload communications to detect potential exploitation attempts
  • Perform a thorough review of the network topology to identify potential exposure
  • Verify that compensating controls are in place for exposed systems
  • Conduct regular asset inventory to ensure all deployments are accounted for
  • Track and document changes to the environment until remediation is verified

Evidence notes

The CVE record was published on 2026-07-15T20:17:51.987Z and was last modified on 2026-07-16T14:16:55.410Z. The NVD entry is currently Undergoing Analysis. The vulnerability has a CVSS score of 5.4 and a severity of MEDIUM.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-56743 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-56743

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-56743 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-56743

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.