CVE-2026-44948: Rancher Fleet Path Traversal Vulnerability

CVE-2026-44948 Overview

CVE-2026-44948 is a path traversal vulnerability [CWE-23] in the ImageScan subsystem of Rancher Fleet. An authenticated attacker with low privileges can traverse outside of the intended directory, causing a denial of service against the Fleet controller. The flaw affects Rancher Fleet versions 0.12.0 through 0.12.16, 0.13.0 through 0.13.12, 0.14.0 through 0.14.7, and 0.15.0 through 0.15.3. The vulnerability is exploitable over the network without user interaction.

Critical Impact
An authenticated attacker can trigger a denial of service in Rancher Fleet GitOps controllers by supplying crafted paths that escape the intended ImageScan working directory.

Affected Products

Rancher Fleet 0.12.0 through 0.12.16
Rancher Fleet 0.13.0 through 0.13.12
Rancher Fleet 0.14.0 through 0.14.7 and 0.15.0 through 0.15.3

Discovery Timeline

2026-06-30 - CVE-2026-44948 published to NVD
2026-07-02 - Last updated in NVD database

Technical Details for CVE-2026-44948

Vulnerability Analysis

Rancher Fleet is a GitOps-at-scale controller that manages continuous delivery of Kubernetes workloads across large fleets of clusters. The ImageScan subsystem periodically scans container image registries and updates deployment manifests based on discovered tags. Fleet writes scan artifacts and intermediate state to a working directory on the controller.

The vulnerability stems from insufficient sanitization of path components processed by the ImageScan subsystem. An authenticated user who can submit ImageScan resources can supply values containing traversal sequences such as ../. Fleet resolves these values relative to its working directory, allowing file operations to reference locations outside of the intended scope.

The impact is limited to availability. According to the vendor advisory, the flaw can crash or destabilize the Fleet controller, disrupting GitOps reconciliation across managed clusters. Confidentiality and integrity are not affected based on the reported scoring.

Root Cause

The root cause is improper limitation of a pathname to a restricted directory, classified as [CWE-23] Relative Path Traversal. Path components sourced from ImageScan resource fields are joined with the controller's working directory without validating that the resulting path remains inside the intended base directory.

Attack Vector

Exploitation requires an authenticated principal with permission to create or modify ImageScan custom resources in a namespace managed by Fleet. The attacker submits an ImageScan object containing crafted path values. When the controller reconciles the resource, it performs file operations against the traversed path and enters an error state, resulting in denial of service. See the Rancher Fleet GitHub Security Advisory for vendor-authoritative details.

Detection Methods for CVE-2026-44948

Indicators of Compromise

ImageScan custom resources containing ../ sequences or absolute path values in fields that are expected to be simple identifiers.
Repeated crash loops or panic stack traces from the fleet-controller pod referencing file I/O operations.
Unexpected file access attempts on the Fleet controller filesystem outside of its designated working directory.

Detection Strategies

Audit Kubernetes API server logs for create and update operations on imagescans.fleet.cattle.io resources and inspect payload contents for traversal patterns.
Monitor fleet-controller pod restart counts and event logs for abnormal termination correlated with ImageScan reconciliation.
Correlate service account activity that submits ImageScan resources against the expected pipeline identities.

Monitoring Recommendations

Enable Kubernetes audit logging at the RequestResponse level for the fleet.cattle.io API group.
Alert on Fleet controller pod restart rates that exceed baseline within a rolling window.
Track filesystem syscall telemetry from Fleet controller nodes for path access outside of the container's expected working directory.

How to Mitigate CVE-2026-44948

Immediate Actions Required

Upgrade Rancher Fleet to a fixed release: 0.12.17, 0.13.13, 0.14.8, or 0.15.4 or later, per the branch in use.
Restrict RBAC so that only trusted automation and administrators can create or modify ImageScan resources.
Review existing ImageScan objects across all managed namespaces and remove any containing traversal sequences.

Patch Information

Rancher has published fixes in the Fleet project. Consult the Rancher Fleet GHSA-c45g-6c2c-rj3p advisory for the exact fixed versions and upgrade guidance. Apply the patched release matching the deployed minor branch to avoid regressing GitOps behavior.

Workarounds

Temporarily disable the ImageScan feature in Fleet if it is not required for the deployment.
Apply Kubernetes admission policies (for example OPA Gatekeeper or Kyverno) that reject ImageScan resources containing .. or absolute path characters in path fields.
Constrain RBAC on the imagescans.fleet.cattle.io resource to a minimal set of service accounts until the patch is applied.

bash

# Kyverno policy example: block ImageScan resources containing path traversal sequences
apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: block-imagescan-path-traversal
spec:
  validationFailureAction: Enforce
  rules:
    - name: deny-traversal-in-imagescan
      match:
        any:
          - resources:
              kinds:
                - ImageScan
      validate:
        message: "ImageScan fields must not contain path traversal sequences."
        pattern:
          spec:
            =(image): "!*../*"
            =(tagName): "!*../*"