CVE-2026-44949: Rancher FleetWorkspace Auth Bypass Issue

CVE-2026-44949 Overview

CVE-2026-44949 is a missing authentication vulnerability [CWE-306] in the Rancher webhook component. The FleetWorkspace admission path allowed side effects to occur inside the rancher-webhook handler. An unauthenticated attacker with network access to the in-cluster rancher-webhook service can submit a crafted admission payload. The attack causes workspace-related Kubernetes objects to be created with attacker-chosen identity data. Affected versions include 0.7.0 through 0.7.10, 0.8.0 through 0.8.7, 0.9.0 through 0.9.6, and 0.10.0 through 0.10.7.

Critical Impact
Unauthenticated network-adjacent attackers can create Kubernetes workspace objects with forged identity attributes, undermining integrity of Rancher-managed clusters.

Affected Products

Rancher webhook versions 0.7.0 up to 0.7.10
Rancher webhook versions 0.8.0 up to 0.8.7, and 0.9.0 up to 0.9.6
Rancher webhook versions 0.10.0 up to 0.10.7

Discovery Timeline

2026-06-30 - CVE-2026-44949 published to NVD
2026-07-02 - Last updated in NVD database

Technical Details for CVE-2026-44949

Vulnerability Analysis

The flaw resides in the admission control path handling FleetWorkspace resources within the Rancher webhook. Kubernetes admission webhooks are intended to validate or mutate incoming API requests. They should not perform authoritative side effects such as creating additional objects. In the affected versions, the FleetWorkspace admission handler creates supporting Kubernetes objects during admission processing. The handler trusts identity fields supplied in the admission payload without independent authentication.

An attacker who can reach the rancher-webhook Service over the cluster network submits a forged AdmissionReview request. The webhook processes the request and generates workspace-related objects populated with attacker-controlled identity data. This impacts integrity of the cluster because subsequent authorization decisions may reference these forged identity attributes.

Root Cause

The root cause is a missing authentication check on the webhook endpoint combined with side-effect-producing behavior inside an admission controller. The handler assumes that requests originate from the Kubernetes API server, but the endpoint accepts admission payloads from any network peer with routing access to the in-cluster Service.

Attack Vector

Exploitation requires network access to the rancher-webhook Service inside the cluster. The attacker crafts an admission review body targeting the FleetWorkspace resource. Because the vulnerable handler does not authenticate the submitter, and because the handler performs writes rather than pure validation, the crafted payload results in creation of workspace objects bearing attacker-chosen identity attributes. No user credentials or Rancher API tokens are required.

See the GitHub Security Advisory GHSA-h83p-cq95-vph4 for the vendor description of the exploitation path.

Detection Methods for CVE-2026-44949

Indicators of Compromise

FleetWorkspace objects or workspace-associated resources created outside of normal GitOps or Rancher UI workflows.
Kubernetes audit log entries showing object creation attributed to unusual user.username or user.groups values propagated from the webhook.
Network connections to the rancher-webhook Service originating from pods or nodes that are not the Kubernetes API server.

Detection Strategies

Enable Kubernetes audit logging on the management cluster and alert on FleetWorkspace create events not preceded by an authenticated Rancher API call.
Baseline expected callers of the rancher-webhook Service and flag any source IP outside that set.
Review webhook access logs for AdmissionReview requests with anomalous userInfo fields.

Monitoring Recommendations

Forward Rancher management cluster audit and webhook logs into a centralized analytics platform for correlation.
Track version inventory of the rancher/webhook deployment across all managed clusters to identify unpatched instances.
Alert on creation of new Fleet workspaces or bindings that reference identities not present in the upstream identity provider.

How to Mitigate CVE-2026-44949

Immediate Actions Required

Upgrade rancher-webhook to a fixed release: 0.7.10, 0.8.7, 0.9.6, or 0.10.7 or later, matching your Rancher channel.
Restrict network reachability of the rancher-webhook Service to the Kubernetes API server using NetworkPolicy.
Review recently created FleetWorkspace objects and remove any not associated with legitimate operator activity.

Patch Information

The Rancher project addressed the issue in webhook releases 0.7.10, 0.8.7, 0.9.6, and 0.10.7. Consult the Rancher webhook security advisory for the corresponding upgrade path aligned to your Rancher Manager version.

Workarounds

Apply a Kubernetes NetworkPolicy that permits ingress to the rancher-webhook pods only from the API server source range.
Temporarily disable the FleetWorkspace validating and mutating webhook configurations if patching cannot be performed and Fleet multi-tenant workspaces are not in use.
Rotate service accounts and review RBAC bindings tied to any workspaces created during the exposure window.

bash

# Example NetworkPolicy restricting access to rancher-webhook
kubectl apply -f - <<'EOF'
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: restrict-rancher-webhook
  namespace: cattle-system
spec:
  podSelector:
    matchLabels:
      app: rancher-webhook
  policyTypes:
    - Ingress
  ingress:
    - from:
        - ipBlock:
            cidr: 10.0.0.0/24  # replace with API server CIDR
      ports:
        - protocol: TCP
          port: 9443
EOF