GHSA-fm8w-2m5w-9j7r BIT-cilium-2026-56743 BIT-cilium-operator-2026-56743 BIT-hubble-relay-2026-56743 CVE-2026-56743 GO-2026-6367

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

Medium Go

Severity: 5.4 / 10; Medium · CVSS 3.1
Exploit chance (EPSS): 0.25%; Chance of exploitation in the next 30 days. Higher than 16.18% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-863 Incorrect Authorization
Fix: 1.19.5; Upgrade github.com/cilium/cilium to this version or later

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 security@cilium.io. This is a private mailing list for the Cilium security team, and the report will be treated as top priority.

Affected versions

Go

Package	Vulnerable	Fixed in
github.com/cilium/cilium	`>= 1.19.0, < 1.19.5`	`1.19.5`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

github.com/cilium/cilium Go → `1.19.5`

go

go get github.com/cilium/cilium@v1.19.5 && go mod tidy

Severity breakdown

CVSS 3.1 5.4

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

Attack vector: Adjacent
Attack complexity: Low
Privileges required: Low
User interaction: None
Scope: Changed
Confidentiality: Low
Integrity: Low
Availability: None

Weakness

CWE-863: Incorrect Authorization

The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.

How to prevent it

Architecture and Design: Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) [REF-229] to enforce the roles at the appropriate boundaries. Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
Architecture and Design: Ensure that access control checks are performed related to the business logic. These checks may be different than the access control checks that are applied to more generic resources such as files, connections, processes, memory, and database records. For example, a database may restrict access for medical records to a specific database user, but each record might only be intended to be accessible to the patient and the patient's doctor [REF-7].
Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
Architecture and Design: For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page. One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.
System Configuration, Installation: Use the access control capabilities of your operating system and server environment and define your access control lists accordingly. Use a "default deny" policy when defining these ACLs.

References

Advisories

nvd.nist.gov/vuln/detail/CVE-2026-56743

Packages

github.com/cilium/cilium

Timeline

Jul 15, 2026 Published
Sep 10, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-w7c2-w76w-5hmj Cilium: Namespaced HTTPRoutes can redirect traffic to other namespaces	High	Also affects github.com/cilium/cilium
GHSA-q6h5-q3q6-f87x CiliumLocalRedirectPolicy addressMatcher allows cross-namespace service traffic hijacking and can break service translation	Medium	Also affects github.com/cilium/cilium
GHSA-3fcv-jvfp-m4q9 Cilium vulnerable to sensitive information disclosure and cluster disruption via local Envoy admin socket access	High	Also affects github.com/cilium/cilium
GHSA-gj49-89wh-h4gj Cillium exposes sensitive information included in the cilium-bugtool debug archive	Medium	Also affects github.com/cilium/cilium
GHSA-hxv8-4j4r-cqgv Cilium L7 proxy may bypass Kubernetes NetworkPolicy for same-node traffic	Medium	Also affects github.com/cilium/cilium
GHSA-5r23-prx4-mqg3 Cilium may not enforce host firewall policies when Native Routing, WireGuard and Node Encryption are enabled	Medium	Also affects github.com/cilium/cilium
GHSA-38pp-6gcp-rqvm Cilium with misconfigured toGroups in policies can lead to unrestricted egress traffic	Medium	Also affects github.com/cilium/cilium
GHSA-5vxx-c285-pcq4 In Cilium, packets from terminating endpoints may not be encrypted in Wireguard-enabled clusters	Medium	Also affects github.com/cilium/cilium

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