Summary
Cilium may unexpectedly allow ingress traffic from the local namespace when a Kubernetes NetworkPolicy is configured with an ipBlock match
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.
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.
The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions. Typical impact: unauthorized data access or execution of privileged operations.
CVE-2026-56743 has a CVSS score of 5.4 (Medium). The vector is reachable from an adjacent network, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.19.5); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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This issue has been patched in:
- Cilium v1.19.5
Releases below v1.19.0 are not affected.
Frequently Asked Questions
- What is CVE-2026-56743? CVE-2026-56743 is a medium-severity incorrect authorization vulnerability in github.com/cilium/cilium (go), affecting versions >= 1.19.0, < 1.19.5. It is fixed in 1.19.5. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
- How severe is CVE-2026-56743? CVE-2026-56743 has a CVSS score of 5.4 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of github.com/cilium/cilium are affected by CVE-2026-56743? github.com/cilium/cilium (go) versions >= 1.19.0, < 1.19.5 is affected.
- Is there a fix for CVE-2026-56743? Yes. CVE-2026-56743 is fixed in 1.19.5. Upgrade to this version or later.
- Is CVE-2026-56743 exploitable, and should I be worried? Whether CVE-2026-56743 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-56743 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-56743? Upgrade
github.com/cilium/ciliumto 1.19.5 or later.