CVE-2026-42965: OpenShift Router SSRF via FQDN EndpointSlice

Technical summary

CVE-2026-42965 is a Server-Side Request Forgery (SSRF) vulnerability in Red Hat OpenShift Router stemming from insufficient validation of FQDN-based EndpointSlices. The vulnerability exploits the router's ability to proxy requests to arbitrary FQDNs when they back a Kubernetes Service. An authenticated user with EndpointSlice write access can create a malicious EndpointSlice that resolves to cloud metadata endpoints (e.g., AWS IMDSv2, Azure Instance Metadata Service, GCP metadata server). The router then proxies client requests to these endpoints, bypassing prior IP-based security controls. This enables credential and metadata disclosure at the network layer.

Business impact

Successful exploitation could lead to unauthorized disclosure of cloud instance credentials, service account tokens, and sensitive instance metadata. In containerized environments where applications often rely on cloud IAM for access control, stolen credentials create a pathway for lateral movement, privilege escalation, and persistent unauthorized access. Organizations running multi-tenant OpenShift clusters face heightened risk, as a single compromised namespace user could extract credentials affecting shared infrastructure and hosted workloads.

Affected systems

Red Hat OpenShift Container Platform and Red Hat OpenShift Router are affected. Vulnerability requires authenticated access with EndpointSlice write permissions; typically held by namespace administrators or service account operators. Single-tenant environments where access controls are strictly managed face lower risk than multi-tenant clusters or those with overly permissive role-based access control (RBAC) policies.

Exploitability

The vulnerability requires local (in-cluster) authentication and explicit write permissions to EndpointSlices, limiting the threat model to authenticated insiders, compromised service accounts, or users with misconfigured RBAC. No exploit is known to be public or weaponized. The attack requires direct interaction with the Kubernetes API, making it difficult to exploit remotely without prior cluster access. However, in environments where namespace users can create or modify Services and EndpointSlices, the technical barrier to exploitation is low.

Remediation

Apply security updates from Red Hat that implement stricter validation of FQDN resolution within EndpointSlices, specifically preventing resolution to known cloud metadata endpoints and internal/private IP address ranges. Additionally, enforce least-privilege RBAC policies to restrict EndpointSlice write permissions only to trusted operators and service accounts. Review and tighten network egress policies to block outbound connections to cloud metadata endpoints from the router namespace.

Patch guidance

Consult Red Hat Security Advisories (RHSA) for OpenShift Container Platform and OpenShift Router for the specific patch versions addressing this vulnerability. Patched versions will include enhanced validation logic that rejects or sanitizes FQDN EndpointSlices pointing to metadata services or private IP ranges. Apply patches according to your maintenance windows, prioritizing cluster administrators and multi-tenant environments. Test patches in non-production clusters first to ensure compatibility with existing Service and EndpointSlice configurations.

Detection guidance

Monitor Kubernetes audit logs for EndpointSlice creation or modification events, particularly those using FQDN-based endpoints pointing to unusual or private domains. Alert on Services backed by FQDNs that resolve to ranges commonly used for cloud metadata (e.g., 169.254.169.254 for AWS, 168.63.129.16 for Azure). Use network observability tools to detect router outbound connections to metadata endpoints. Implement webhook admission controllers to block or warn on suspicious EndpointSlice patterns in production namespaces.

Why prioritize this

This vulnerability merits immediate attention due to its HIGH severity score, the sensitive nature of cloud credentials, and the potential for significant lateral movement in containerized environments. Although it requires authentication, the combination of widespread cloud metadata exposure and the ease of exploitation by any user with basic EndpointSlice permissions makes it a credible internal threat. Organizations should patch before granting broad EndpointSlice write access or before operating multi-tenant clusters.

Risk score, explained

CVSS 3.1 score of 7.7 reflects a HIGH-severity issue with network-based attack vector, low attack complexity, and low privilege requirements balanced against local authentication requirements. The high confidentiality impact (C:H) reflects the sensitive nature of credentials and metadata at risk. No integrity or availability impact is scored, as the vulnerability enables read-only access to sensitive information without compromising data integrity or service availability.

Frequently asked questions