CVE-2026-13322
Description
A flaw was found in KubeVirt's downward metrics virtio-serial server. The server reads guest requests using textproto.Reader.ReadLine(), which buffers input indefinitely until a newline character is received, with no length limit or read deadline. A user with access to a VM guest that has the downward metrics virtio-serial device configured can write a continuous byte stream to the device, causing unbounded memory allocation in the virt-handler process until it is OOM-killed.
Statement
Red Hat has rated this issue as having Low security impact. The vulnerable code runs in virt-handler, a node-level DaemonSet; however, in OpenShift Virtualization, cgroup memory limits ensure the OOM kill is contained to the virt-handler pod and does not affect the node kernel or kubelet. Running VM workloads (QEMU processes) survive independently and continue operating — only management operations (live migration, graceful shutdown, monitoring updates) are temporarily disrupted. An administrator can recover by deleting the offending VirtualMachineInstance, after which virt-handler resumes normal operation on its next restart. The attack surface is limited to VMIs that explicitly configure a downwardMetrics virtio-serial device, which is not part of the default VM configuration. The blast radius is confined to a single node.
Mitigation
The downward metrics virtio-serial device must be explicitly added to a VM's specification to be present. Clusters that do not use this feature are not exposed. To reduce exposure, administrators can restrict the ability to configure downward metrics devices on tenant VMs by using an admission webhook or policy controller such as Gatekeeper/OPA.
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 | 3.8 | N/A | N/A |
| Attack Vector | Local | N/A | N/A |
| Attack Complexity | Low | 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 | None | N/A | N/A |
| Integrity Impact | None | N/A | N/A |
| Availability Impact | Low | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:L
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory); DoS: Resource Consumption (Other)
When allocating resources without limits, an attacker could prevent other systems, applications, or processes from accessing the same type of resource. It can be easy for an attacker to consume many resources by rapidly making many requests or causing larger resources to be used than is needed.
Acknowledgements
This issue was discovered by Huzaifa Sidhpurwala (Red Hat).
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