CVE-2026-50566: Fission Privilege Escalation Vulnerability

CVE-2026-50566 Overview

Fission is an open-source, Kubernetes-native serverless framework for deploying functions and applications on Kubernetes clusters. CVE-2026-50566 affects Fission versions prior to 1.24.0 and allows tenants with environments.fission.io create/update RBAC permissions to escape container isolation. Attackers can run privileged containers, containers with allowPrivilegeEscalation, or containers with dangerous Linux capabilities in the Fission function or builder namespace. These containers execute under the executor's high-privilege service account, enabling host filesystem access, network access, and node- or cluster-level compromise. The vulnerability is tracked as [CWE-250] (Execution with Unnecessary Privileges) and was patched in version 1.24.0.

Critical Impact
A tenant with limited Fission RBAC can break container isolation and pivot to full Kubernetes cluster compromise through abuse of the executor service account.

Affected Products

Fission versions prior to 1.24.0
Kubernetes clusters running vulnerable Fission deployments
Multi-tenant environments granting environments.fission.io create/update RBAC

Discovery Timeline

2026-06-10 - CVE-2026-50566 published to NVD
2026-06-10 - Last updated in NVD database

Technical Details for CVE-2026-50566

Vulnerability Analysis

Fission's executor component schedules pods for user-defined environments and builders using a high-privilege service account. Prior to version 1.24.0, the controller did not validate or restrict the pod security fields submitted in Environment resources. A tenant authorized to create or update environments.fission.io objects could declare containers with securityContext.privileged: true, allowPrivilegeEscalation: true, or dangerous Linux capabilities such as CAP_SYS_ADMIN. The executor would then schedule those pods in the function or builder namespace under its own service account, granting the attacker container-sandbox escape and access to host resources.

Root Cause

The root cause is missing admission-time validation of pod security parameters defined inside Environment custom resources. Fission treated environment specifications as trusted while binding them to a service account with broad cluster permissions. This combination of unfiltered user input and over-privileged execution context maps directly to [CWE-250]: Execution with Unnecessary Privileges.

Attack Vector

An authenticated tenant with create or update rights on environments.fission.io submits a crafted Environment manifest. The manifest references a container image controlled by the attacker and sets privileged: true or adds dangerous capabilities. When the executor instantiates the function or builder pod, the container runs with host-level access. From there, the attacker can mount the host filesystem, access the kubelet credentials, reach the Kubernetes API as a node, and pivot laterally across the cluster.

No verified proof-of-concept exploit code is available. Technical specifics are documented in the GitHub Security Advisory GHSA-m63v-2g9w-2w6v and GitHub Pull Request #3406.

Detection Methods for CVE-2026-50566

Indicators of Compromise

Pods in Fission function or builder namespaces running with securityContext.privileged: true or allowPrivilegeEscalation: true
Containers requesting Linux capabilities such as CAP_SYS_ADMIN, CAP_NET_ADMIN, or CAP_SYS_PTRACE
Environment custom resources referencing untrusted container images or unusual command overrides
Unexpected access to host paths, /var/run/docker.sock, or kubelet credentials from function pods

Detection Strategies

Audit Kubernetes API server logs for create and update actions against environments.fission.io resources
Inspect running pods in Fission namespaces for elevated securityContext fields and capability grants
Correlate executor service account token usage with pod creation events outside normal patterns

Monitoring Recommendations

Enable Kubernetes audit logging at the RequestResponse level for the Fission namespaces
Deploy Pod Security Admission in enforce mode with a restricted profile on Fission function and builder namespaces
Stream pod runtime telemetry into a centralized data lake for behavioral analysis of container escape attempts

How to Mitigate CVE-2026-50566

Immediate Actions Required

Upgrade Fission to version 1.24.0 or later in all clusters
Review existing Environment resources for privileged settings and remove untrusted entries
Restrict RBAC so only trusted operators hold create and update rights on environments.fission.io
Rotate the executor service account token if abuse is suspected

Patch Information

The fix is included in Fission v1.24.0. Refer to the GitHub Release v1.24.0 and the corresponding GitHub Pull Request #3406 for code-level changes. The patch enforces validation of pod security fields in Environment specifications before the executor schedules workloads.

Workarounds

Apply Pod Security Admission restricted profile to Fission function and builder namespaces to block privileged pods
Use an admission controller such as OPA Gatekeeper or Kyverno to reject Environment objects with privileged or capability-elevating fields
Scope the executor service account to the minimum permissions required and isolate Fission tenants per namespace

bash

# Kyverno policy snippet to reject privileged Fission environments
apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: block-privileged-fission-envs
spec:
  validationFailureAction: enforce
  rules:
    - name: deny-privileged
      match:
        resources:
          kinds:
            - environments.fission.io/v1
      validate:
        message: "Privileged containers are not allowed in Fission Environments"
        pattern:
          spec:
            runtime:
              container:
                securityContext:
                  privileged: "false"
                  allowPrivilegeEscalation: "false"