CVE-2026-13434
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).
Statement
Red Hat has assessed this flaw as Moderate impact for OpenShift Virtualization. The vulnerability requires the ExternalNetResourceInjection Beta feature gate to be explicitly enabled by a cluster administrator — this gate is off by default in all shipped versions of OpenShift Virtualization. When the gate is disabled (the default configuration), the NAD lookup in virt-controller catches invalid network names (bracket-containing strings fail Kubernetes object name validation), and pod rendering is blocked. Environments that have not explicitly enabled this feature gate are not vulnerable. The ExternalNetResourceInjection feature gate was introduced in KubeVirt v1.8.0 and first shipped in OpenShift Virtualization 4.21; earlier versions are not affected. For environments where the gate is enabled, a tenant with standard VM creation permissions (kubevirt.io:edit) could gain network access to segments in other namespaces, though actual data access depends on what services are reachable on those networks and whether NetworkPolicy is enforced on the target segments.
Mitigation
If the ExternalNetResourceInjection feature gate has been enabled, disable it by removing it from the HyperConverged CR's spec.featureGates configuration. This restores the NAD lookup that blocks malformed network names. If the feature gate is required for operational reasons, restrict kubevirt.io:edit permissions to trusted users only and enforce NetworkPolicy on sensitive network segments to limit lateral movement from unauthorized attachments.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 4.9 | N/A | N/A |
| Attack Vector | Network | N/A | N/A |
| Attack Complexity | High | N/A | N/A |
| Privileges Required | Low | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Changed | N/A | N/A |
| Confidentiality | Low | N/A | N/A |
| Integrity Impact | Low | N/A | N/A |
| Availability Impact | None | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:L/I:L/A:N
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory)
An attacker could provide unexpected values and cause a program crash or arbitrary control of resource allocation, leading to excessive consumption of resources such as memory and CPU.
Confidentiality
Technical Impact: Read Memory; Read Files or Directories
An attacker could read confidential data if they are able to control resource references.
Integrity,Confidentiality,Availability
Technical Impact: Modify Memory; Execute Unauthorized Code or Commands
An attacker could use malicious input to modify data or possibly alter control flow in unexpected ways, including arbitrary command execution.
Acknowledgements
This issue was discovered by Huzaifa Sidhpurwala (Red Hat).
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