CVE-2026-49821: Fission: Cross-namespace Environment reference in Package allows build-time command execution and SA token exfiltration

Synopsis

A missing namespace-validation check in Fission's buildermgr controller allows an authenticated user to craft a Package custom resource that references an Environment from a foreign namespace. The attack travels over the network and requires a low-privilege Kubernetes account, with no victim interaction needed. Successful exploitation gives the attacker read access to sensitive data, including build-time command execution output and Kubernetes service-account tokens belonging to the targeted namespace. HarborGuard tracks this advisory and will make a patched-image rebuild available the moment an upstream fix is published.

HarborGuard Coverage

Exploit Conditions

• Network reachabilityRequired

  The attacker must reach the Kubernetes API server over the network to submit the malicious Package CRD.

• AuthenticationRequired

  Any low-privilege Kubernetes account with permission to create or modify Package resources is sufficient; no administrative role is needed.

• Victim interactionNot required

  No user action is required; the buildermgr controller processes the malicious Package automatically on creation.

• Attack complexityDetail

  Exploitation is reliable and condition-free; the attacker only needs to supply a Package manifest referencing a foreign Environment namespace.

Blast Radius

• Reads Kubernetes service-account tokens associated with the target namespace, enabling further lateral movement within the cluster.
• Reads build-time output and any secrets injected into the builder environment belonging to the cross-namespace Environment.
• Bypasses namespace-level isolation boundaries, exposing resources in namespaces the attacker has no direct permission to access.