Fission EUVD-2026-36101

Exploitation requires the attacker to hold high-privilege access within Fission (CVSS PR:H confirmed), specifically the ability to create or modify Fission builder environments that cause the buildermgr to invoke createBuilderDeployment and schedule a builder pod. The vulnerability is triggered when Fission version prior to 1.24.0 is running and a builder environment referencing a user-supplied container image is registered or updated. The attacker must control the builder container image (or influence its contents) to exfiltrate the mounted token during build execution. Exploitation is limited by: (1) the PR:H CVSS requirement - only users with elevated Fission control-plane access can register builder environments; (2) the actual impact being bounded by the RBAC permissions granted to the fission-builder service account, which are deployment-specific; and (3) scope being unchanged (S:U), meaning lateral movement beyond fission-builder's existing permissions requires additional steps not covered by this CVE. The vulnerability does not affect function runner pods, only builder pods - deployments that do not use the Fission builder workflow (e.g., pre-built environments with no source build step) are not exposed.

The CVSS base score of 4.9 (Medium) reflects the combination of network-reachable attack vector (AV:N), low complexity (AC:L), high privilege requirement (PR:H), no user interaction (UI:N), unchanged scope (S:U), and high confidentiality impact (C:H) with no integrity or availability impact. The PR:H constraint is the primary risk-limiting factor: exploitation requires an actor who already holds elevated permissions within the Fission control plane - specifically the ability to create or modify builder environments that trigger builder pod creation. This substantially narrows the exploitable population compared to a network-unauthenticated finding. The S:U (Unchanged scope) rating is notable because the token exposure could grant access to Kubernetes API resources beyond the Fission namespace depending on the fission-builder service account's cluster RBAC bindings, though CVSS scope does not capture this lateral movement potential. No EPSS score was provided in the input data, so exploitation probability cannot be quantified from that signal. The vulnerability is not listed in the CISA KEV catalog, and no public POC exploit code has been identified. Real-world risk is moderate for multi-tenant or shared Fission clusters where the fission-builder service account holds meaningful cluster permissions, and lower for single-tenant deployments with minimal RBAC grants. The absence of an integrity impact rating means direct cluster resource modification via this token would depend on the specific RBAC policy bound to fission-builder, which is deployment-specific and not confirmed by available data.

An attacker with high-privilege access to a Fission deployment - such as a developer authorized to register builder environments - submits a builder environment referencing a malicious container image under their control. When Fission's buildermgr creates the builder pod, the kubelet automatically mounts the fission-builder service account token into the malicious container at /var/run/secrets/kubernetes.io/serviceaccount/token. The attacker's code reads this token during the build phase and uses it to authenticate to the Kubernetes API server, querying or modifying cluster resources permitted by the fission-builder service account's RBAC bindings - potentially including secrets, configmaps, or pod management within the Fission namespace. No public POC has been identified, but the attack requires only standard Kubernetes API client libraries and knowledge of the well-known token mount path.