CVE-2026-44882: Portainer: Kubernetes middleware continues after token validation failure, bypassing endpoint authorization

Synopsis

An authorization bypass vulnerability exists in Portainer (Community Edition and Enterprise Edition) versions 2.33.0 through 2.33.7, caused by a missing return statement in the Kubernetes middleware layer (kubeClientMiddleware). After token validation fails, the middleware writes a 403 response but continues executing, forwarding the request to the Kubernetes cluster with a nil token value instead of halting. A logged-in user who lacks permission to access a specific Kubernetes endpoint can exploit this to reach that endpoint anyway, reading cluster data or modifying Kubernetes resources they should be blocked from. HarborGuard tracks this advisory and will make a patched-image rebuild available as soon as an upstream fix version is published.

HarborGuard Coverage

Exploit Conditions

• Network reachabilityRequired

  The attacker must reach the Portainer service over the network, as the vulnerability is exposed via Portainer's HTTP API endpoints.

• AuthenticationRequired

  A valid Portainer session is required; any low-privilege account with a session token is sufficient to trigger the bypass.

• Victim interactionNot required

  No victim interaction is needed; the attacker sends requests directly to the Portainer API without involving another user.

• Attack complexityDetail

  Exploit conditions are straightforward and reliable, requiring no race condition or special environmental setup beyond holding a valid Portainer session.

Blast Radius

• An attacker reads Kubernetes cluster data, such as pod specs, secrets, config maps, and service account tokens, from endpoints they are not authorized to access.
• An attacker modifies Kubernetes resources, such as deployments, roles, or configurations, across endpoints their Portainer permissions should block.
• The bypass is scoped to Kubernetes endpoints behind the flawed middleware, so direct access to Docker or Swarm environments managed by the same Portainer instance is not affected by this specific defect.