CVE-2026-40923: 
Wolfi vulnerability analysis and mitigation

CVE-2026-40923 is a path traversal vulnerability in Tekton Pipelines (Linux Foundation) that allows authenticated users to bypass VolumeMount path restrictions protecting internal /tekton/ directories. The flaw was disclosed on April 21, 2026, and affects all versions of github.com/tektoncd/pipeline through v1.10.0 across both the v1 and v1beta1 APIs. It carries a CVSS v3.1 base score of 5.4 (Medium) (Github Advisory, Tekton Advisory).

The root cause is a missing call to filepath.Clean before the strings.HasPrefix check in the VolumeMount path validation logic, classified as CWE-22 (Path Traversal). The vulnerable code in pkg/apis/pipeline/v1/container_validation.go (and its v1beta1 counterpart) rejects paths starting with /tekton/ unless they begin with /tekton/home, but does not normalize the path first. An attacker can craft a mount path such as /tekton/home/../results, which passes both prefix checks at admission time but resolves to /tekton/results at runtime when the container runtime processes the .. component. Exploitation requires only low privileges (Task or TaskRun creation permissions) and no user interaction (Github Advisory, Tekton Advisory).

An authenticated user who can create Task or TaskRun resources can mount arbitrary volumes over internal Tekton execution paths, resulting in low confidentiality and integrity impacts with no availability impact. Concrete consequences include writing fake task results that downstream pipelines trust, reading or modifying step scripts before execution, and interfering with entrypoint coordination state. In multi-tenant CI/CD environments, this could enable pipeline result forgery or supply chain manipulation affecting downstream consumers of pipeline outputs (Github Advisory).

No public proof-of-concept exploit code or evidence of in-the-wild exploitation has been reported. The EPSS score is approximately 0.052% (16th percentile), indicating a low near-term exploitation probability. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. Exploitation requires authenticated access with Task or TaskRun creation permissions, limiting the attack surface to users already operating within a Tekton-enabled Kubernetes cluster (Github Advisory).

1. Gain authenticated access: Obtain credentials or a service account with permissions to create Task or TaskRun resources in a Kubernetes namespace running a vulnerable version of Tekton Pipelines (≤ v1.10.0).
2. Craft a malicious Task definition: Define a Task spec that includes a VolumeMount with a path using .. traversal, such as mountPath: /tekton/home/../results, to bypass the prefix validation check.
3. Submit the Task or TaskRun: Apply the crafted manifest via kubectl apply -f malicious-task.yaml. The admission webhook validates the path as /tekton/home/../results, which passes the strings.HasPrefix check for the allowed /tekton/home prefix.
4. Runtime path resolution: When the container runtime starts the pod, it resolves .. and mounts the attacker-controlled volume at /tekton/results (or another restricted internal path).
5. Achieve objective: Write forged task results to /tekton/results to manipulate downstream pipeline decisions, or read/overwrite step scripts at /tekton/scripts to influence execution behavior (Github Advisory, Tekton Advisory).

• Kubernetes API Logs: Audit log entries showing create or apply operations on Task or TaskRun resources containing volumeMounts with mountPath values that include .. components (e.g., /tekton/home/../results).
• Pod Spec Inspection: Running pods with VolumeMount paths containing .. traversal sequences targeting /tekton/ subdirectories; inspect with kubectl get pod <name> -o yaml.
• File System: Unexpected files or modified content in /tekton/results, /tekton/scripts, or other internal Tekton directories within task runner containers.
• Pipeline Behavior: Downstream pipeline steps consuming unexpected or malformed task results that differ from what the upstream task step actually produced.

Upgrade to one of the patched versions: v1.11.1, v1.9.3, v1.6.2, v1.3.4, or v1.0.2, depending on the release branch in use. As an interim workaround, deploy admission controllers such as OPA/Gatekeeper or Kyverno with policies that reject VolumeMount paths containing .. components. Additionally, restrict Task and TaskRun creation permissions via Kubernetes RBAC to only trusted users, particularly in multi-tenant environments (Github Advisory, v1.11.1 Release).

The vulnerability was reported by community researcher @kodareef5 and remediated by Tekton maintainer vdemeester with review by aThorp96, reflecting a standard coordinated disclosure process within the Tekton open source community. The advisory was published simultaneously to the GitHub Advisory Database and NVD on April 21, 2026. No significant broader media coverage or notable external researcher commentary has been identified beyond standard CVE tracking feeds (Github Advisory).