Summary
Fission: Environment Runtime.Container and Builder.Container SecurityContext bypass allows privileged pod creation
A follow-up bypass of the round-4 PodSpec hardening (GHSA-gx55-f84r-v3r7, GHSA-wmgg-3p4h-48x7, GHSA-v455-mv2v-5g92). Those advisories validate and sanitize the PodSpec (spec.runtime.podSpec / spec.builder.podSpec /function.spec.podSpec), but the Environment CRD also exposes spec.runtime.container and spec.builder.container, a standalone Container merged into the runtime/builder pod whose SecurityContext bypassed both layers.
Details
Admission-layer gap. Environment.Validate() calls ValidatePodSpecSafety() on Runtime.PodSpec and Builder.PodSpec only. That function takes a *PodSpec, so it never inspects the standalone Runtime.Container.SecurityContext
or Builder.Container.SecurityContext.
Merge-layer gap. sanitizeContainerSecurityContext() ran only inside MergePodSpec(). The container field is merged via MergeContainer(), which did not sanitize. With only Runtime.Container set and Runtime.PodSpec nil,MergePodSpec is never invoked, so the sanitizer never ran.
Affected merge sites: poolmgr (gp_deployment.go), newdeploy (newdeploy.go), and buildermgr (envwatcher.go).
Proof of concept
apiVersion: fission.io/v1
kind: Environment
metadata:
name: priv-escape-test
namespace: default
spec:
version: 3
runtime:
image: "ghcr.io/fission/python-env:latest"
container:
name: priv-escape-test
securityContext:
privileged: true
poolsize: 1
The admission webhook accepts this Environment and the resulting pool pod runs with privileged: true. Equivalent bypasses: allowPrivilegeEscalation: true, capabilities.add: ["SYS_ADMIN"], capabilities.add: ["NET_ADMIN","SYS_PTRACE"]. The same attack applies to Builder.Container.
Workarounds
- Restrict Environment create/update RBAC to trusted administrators.
- Deploy a Kyverno / OPA Gatekeeper policy rejecting dangerous Container SecurityContext on Environment CRDs.
- Label the function/builder namespaces with
pod-security.kubernetes.io/enforce: restricted.
References
- GHSA-gx55-f84r-v3r7, GHSA-wmgg-3p4h-48x7, GHSA-v455-mv2v-5g92, the round-4 PodSpec fixes this advisory bypasses (#3391,
e484df84).
Impact
A tenant with environments.fission.io create/update RBAC can run privileged / allowPrivilegeEscalation / dangerous-capability containers in the Fission function or builder namespace, scheduled under the executor's high-privilege
service account, enabling container-sandbox escape, host filesystem and network access, and potential node- and cluster-level compromise. Identical blast radius to GHSA-gx55-f84r-v3r7.
The application assigns, modifies, tracks, or checks privileges incorrectly, allowing a user to gain elevated access. Typical impact: privilege escalation beyond the intended level.
CVE-2026-50566 has a CVSS score of 9.9 (Critical). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.24.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Fixed in #3406 and released in v1.24.0.
- Admission layer (primary defence): a new
ValidateContainerSafetyinpkg/apis/core/v1/podspec_safety.goapplies the per-container SecurityContext denylist (privileged,allowPrivilegeEscalation, dangerous capabilities) to a
standalone container, and is called fromEnvironment.Validate()forRuntime.ContainerandBuilder.Container. - Merge layer (defence in depth):
sanitizeContainerSecurityContext()is now invoked insideMergeContainer()itself, covering all three executor/builder call sites.
Frequently Asked Questions
- What is CVE-2026-50566? CVE-2026-50566 is a critical-severity improper privilege management vulnerability in github.com/fission/fission (go), affecting versions <= 1.23.0. It is fixed in 1.24.0. The application assigns, modifies, tracks, or checks privileges incorrectly, allowing a user to gain elevated access.
- How severe is CVE-2026-50566? CVE-2026-50566 has a CVSS score of 9.9 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of github.com/fission/fission are affected by CVE-2026-50566? github.com/fission/fission (go) versions <= 1.23.0 is affected.
- Is there a fix for CVE-2026-50566? Yes. CVE-2026-50566 is fixed in 1.24.0. Upgrade to this version or later.
- Is CVE-2026-50566 exploitable, and should I be worried? Whether CVE-2026-50566 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-50566 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-50566? Upgrade
github.com/fission/fissionto 1.24.0 or later.