CVE-2026-50566: Fission: Environment Runtime.Container and Builder.Container SecurityContext bypass allows privileged pod creation

Should you act?

Critical, preconditions apply

Severe if exploited, but exploitation needs conditions that may not apply to you. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.5%, percentile 42: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 42% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Needs an account (low (any account)). Exposure depends on who can log in.
• Only applies if your dependency tree includes github.com/fission/fission (Go) <= 1.23.0, fixed in 1.24.0. Check your lockfile, including transitive dependencies.

What it is

Fission is an open-source, Kubernetes-native serverless framework that simplifies the deployment of functions and applications on Kubernetes. Prior to version 1.24.0, 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. This issue has been patched in version 1.24.0.

From the GitHub advisory

Summary

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.

Weakness type: CWE-250, CWE-269.

Product: github.com/fission/fission (Go) · Assigned by: GitHub_M · Published: 2026-06-10

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: low (any account)
• User interaction: none
• Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.51% probability of exploitation activity in the next 30 days; percentile 42.

Timeline

• 2026-06-10 — CVE record published by GitHub_M
• 2026-06-12 — CVE record last updated
• 2026-06-30 — GitHub-reviewed advisory GHSA-m63v-2g9w-2w6v published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-m63v-2g9w-2w6v github.com
2. CVE.org record CVE-2026-50566 cve.org
3. NVD entry CVE-2026-50566 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com
4. github.com github.com

Critical Go advisories · Today’s Security Digest