CVE-2026-49823: Fission: Cross-namespace Package read via unvalidated PackageRef in Function admission webhook

Synopsis

This is an authorization bypass vulnerability in Fission, the Kubernetes-native serverless framework. A low-privileged, authenticated user can craft a Function spec that references a Package in a namespace they do not have access to, bypassing the admission webhook's namespace validation. Successful exploitation lets the attacker read the contents of any Fission Package across all namespaces in the cluster, including potentially sensitive build artifacts and source code. No fix version has been published yet; HarborGuard tracks the upstream advisory and will make a patched-image rebuild available as soon as a fix is released.

HarborGuard Coverage

Exploit Conditions

• Network reachabilityRequired

  The Fission admission webhook is exposed over the network, so an attacker must be able to reach the Kubernetes API server (and by extension the webhook) across the network.

• AuthenticationRequired

  The attacker must hold a low-privilege Kubernetes account with enough RBAC permission to create or update Function resources; unauthenticated access is not sufficient.

• Victim interactionNot required

  No human target needs to take any action; the attacker submits a crafted Function spec directly to the API server.

• Attack complexityDetail

  Exploitation is reliable and condition-free: the attacker only needs to set PackageRef.Namespace to a target namespace in a Function spec, with no race conditions or special environmental state required.

Blast Radius

• Reads the full contents of any Fission Package object in any namespace in the cluster, regardless of the attacker's own namespace permissions.
• Exposes build artifacts, compiled function binaries, and source archives stored inside those Package objects.
• Reveals namespace names and Package metadata, giving the attacker a map of the cluster's function workloads for further targeting.