Executive Summary

CVE-2026-50545 is a critical security vulnerability in Fission, a Kubernetes-native serverless framework. The issue arises from insufficient validation of certain pod specification fields (`Environment.spec.runtime.podSpec` and `spec.builder.podSpec`), which allowed attackers to inject dangerous configurations into pods.

Specifically, builder pods were auto-mounting the fission-builder ServiceAccount token into user-supplied builder containers. Since this ServiceAccount had namespace-wide read permissions, malicious builder images could access all Secrets and ConfigMaps in the builder namespace.

Additionally, the vulnerability involved three flaws: incomplete validation in the environment validation process, a webhook bypass due to restricted verbs, and unconditional propagation of risky pod fields such as hostPID, hostIPC, hostNetwork, hostPath, and privileged settings. This allowed attackers to create privileged pods with host-root mounts, enabling them to access sensitive cluster credentials and potentially take over the entire Kubernetes cluster.

The vulnerability was fixed in version 1.24.0 by disabling the default auto-mounting of the ServiceAccount token in user containers, restricting it only to a fetcher sidecar container, improving validation, and preventing unsafe pod specification merges.

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Impact Analysis

This vulnerability can have severe impacts including full cluster compromise. An attacker exploiting this flaw can escalate privileges by creating privileged pods with host-root mounts, gaining access to the cluster's CA private key.

With these capabilities, the attacker can sign arbitrary kubelet certificates, effectively taking over the entire Kubernetes cluster.

The vulnerability also allows malicious builder images to access all Secrets and ConfigMaps within the builder namespace, exposing sensitive information.

Overall, the impact includes node escape, confidentiality, integrity, and availability breaches, leading to complete cluster takeover and significant security risks.

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Detection Guidance

Detection of this vulnerability involves checking for the presence of unsafe pod specifications in Fission environments, particularly looking for pods that have auto-mounted the fission-builder ServiceAccount token or contain dangerous fields such as hostPID, hostIPC, hostNetwork, hostPath, or privileged settings.

You can inspect the pod specifications in the builder namespace to see if the fission-builder ServiceAccount token is auto-mounted in user builder containers. Additionally, review Environment resources for suspicious podSpec configurations that include privileged or host-level access.

Suggested commands include:

• kubectl get pods -n <builder-namespace> -o json | jq '.items[] | select(.spec.serviceAccountName=="fission-builder") | {name: .metadata.name, automountServiceAccountToken: .spec.automountServiceAccountToken, containers: .spec.containers[].name}'
• kubectl get environments -o yaml | grep -E 'hostPID|hostIPC|hostNetwork|hostPath|privileged'
• kubectl get pods -n <builder-namespace> -o json | jq '.items[] | select(.spec.containers[].volumeMounts[]?.name == "fission-builder-token")'

These commands help identify pods that may have been created or patched with unsafe configurations or have the ServiceAccount token improperly mounted, indicating potential exploitation of the vulnerability.

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Mitigation Strategies

The primary mitigation step is to upgrade Fission to version 1.24.0 or later, where the vulnerability has been patched.

The patch disables the default auto-mounting of the fission-builder ServiceAccount token in user builder containers and restricts it only to the fetcher sidecar container, preventing unauthorized access to Secrets and ConfigMaps.

Additional safeguards include improved validation of Environment pod specifications to block dangerous fields and prevent webhook bypasses.

Until the upgrade is applied, you should audit and remove any Environment or pod specifications that include privileged or host-level access fields, and ensure that builder pods do not have the ServiceAccount token auto-mounted.

Consider restricting permissions of the fission-builder ServiceAccount to minimize potential impact.

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Compliance Impact

CVE-2026-50545 allows attackers to escalate privileges and gain full cluster takeover in Kubernetes environments running Fission. This leads to unauthorized access to sensitive data, including cluster CA private keys and potentially all Secrets and ConfigMaps in the namespace. Such unauthorized access and control can result in breaches of confidentiality, integrity, and availability of data.

Because of these impacts, organizations using vulnerable versions of Fission may face compliance risks with standards like GDPR and HIPAA, which require strict controls over access to sensitive personal and health data. The vulnerability could lead to data breaches or unauthorized data exposure, violating these regulations' requirements for data protection and security.

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