CVE-2026-41053: Rancher has over-inclusive team membership expansion in GitHub App authentication provider

A vulnerability has been identified within Rancher Manager in the GitHub App authentication provider. When evaluating permissions, the provider incorrectly expands user team memberships to include all teams within the associated GitHub organization, rather than restricting access to the specific teams to which the user actually belongs.

Specifically, when a user authenticates via the GitHub App provider, Rancher’s team membership evaluation logic incorrectly handles cached data. Instead of checking the user-specific list, the evaluation logic iterates over all teams defined within the entire GitHub organization. The authentication provider should consult the correctly cached, per-user membership list to assign the user’s specific group permissions. Consequently, any authenticated user who belongs to at least one team in a GitHub organization is mistakenly granted group principals for every team within that entire organization during authentication and authorization checks.

This issue allows a malicious user who is a member of a low-privilege team within a GitHub organization to gain unauthorized access to or permissions for any other team in that organization. If those other teams are bound to Rancher login allowlists or RBAC roles (cluster-level, project-level, or global), the attacker can pass access checks that should otherwise fail, inheriting permissions they were never granted.

Exploitation of this vulnerability requires the following conditions to be met:

• The GitHub App authentication provider must be enabled and configured for the target GitHub organization.
• The attacker must possess a valid GitHub account with membership in at least one team within that target organization.
• A separate team within the same GitHub organization must be explicitly mapped to Rancher RBAC roles or specified within Rancher’s login allowlist (allowedPrincipalIds).

Please consult the associated MITRE ATT&CK - Technique - Valid Accounts for further information about this category of attack.