CVE-2026-13434: Virt-controller-rhel9: kubevirt: kubevirt: multus default-network annotation injection via unvalidated tenant networkname when externalnetresourceinjection is enabled

Vulnerability summary

CVE-2026-13434 is a medium (CVSS 4.9) Improper Input Validation vulnerability in kubevirt. EPSS estimates a 0.24% chance of exploitation in the next 30 days, higher than 15.7% of scored vulnerabilities.

Timeline

1. 26-06-2026
   PublishedVulnerability first disclosed.
2. 27-06-2026
   Last modifiedVulnerability information updated.

Description

A flaw was found in KubeVirt's network annotation generator. When a tenant creates a VirtualMachineInstance with a Multus network configuration, the supplied networkName value is written verbatim into the launcher pod's v1.multus-cni.io/default-network annotation without format validation or sanitization. The only admission check rejects empty strings; no DNS-1123 format validation, JSON detection, or special character rejection is performed. When the ExternalNetResourceInjection Beta feature gate is enabled (off by default, cluster-admin only), the NAD lookup that would otherwise catch malformed names is skipped by design. A tenant with kubevirt.io:edit permissions can inject a JSON-formatted NetworkSelectionElement array specifying an arbitrary namespace, NAD name, static IP address, and MAC address. Multus on the node parses this JSON and attaches the launcher pod to the specified network attachment in any namespace, enabling cross-namespace network access and IP/MAC impersonation on network segments normally segregated from tenant workloads. The ExternalNetResourceInjection feature gate was introduced in KubeVirt v1.8.0 (first shipped in OpenShift Virtualization 4.21).

• CWE-20Improper Input ValidationThe product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.