CVE-2026-49824: Fission: Cross-namespace Environment reference via unvalidated EnvironmentRef in Function admission webhook

Synopsis

This is an authorization bypass in Fission, the Kubernetes-native serverless framework, affecting versions prior to 1.24.0. The Function admission webhook validates that referenced Secrets and ConfigMaps stay within the function's own namespace, but applies no equivalent check to the spec.environment.namespace field, allowing any authenticated user with function-creation rights to reference an Environment object in a different namespace. Successful exploitation lets an attacker read a high-confidentiality cross-namespace Environment resource and make limited modifications, breaking the namespace isolation that Kubernetes tenancy models depend on. No fix version has been published upstream yet; HarborGuard is tracking the advisory for patch availability.

HarborGuard Coverage

Exploit Conditions

• Network reachabilityRequired

  The Fission API server and admission webhook are exposed over the network, so an attacker must be able to reach the Kubernetes API endpoint to submit a crafted Function resource.

• AuthenticationRequired

  Any low-privilege account with permission to create or update Function resources in at least one Fission namespace is sufficient to trigger the missing validation check.

• Victim interactionNot required

  No victim interaction is needed; the attacker submits a Function spec directly to the API server and the flawed webhook logic executes automatically.

• Attack complexityDetail

  Exploit conditions are straightforward and reliable; the attacker simply sets spec.environment.namespace to an arbitrary target namespace with no race conditions or environmental prerequisites required.

Blast Radius

• Attacker reads the full contents of an Environment object in an otherwise inaccessible namespace, which may include runtime container image references, build configuration, and environment-specific secrets embedded in the spec.
• Attacker makes limited writes to the referenced Environment resource, potentially altering the runtime image or resource limits used by functions in the target namespace.
• Kubernetes namespace boundaries between tenants or teams are silently bypassed, undermining any multi-tenant isolation model built on namespace-scoped RBAC.
• No availability impact is introduced directly; the affected service continues running while the unauthorized cross-namespace access occurs.