Apache Pulsar: Original principal of proxied requests authorized with the proxy's authentication data, allowing privilege escalation

Overview

When a configured proxy role sends a request to the broker on behalf of another user (the original principal), the broker is designed to authorize both the proxy role and the original principal and to allow the request only if both are authorized, so that the original principal cannot exceed its own permissions. Two flaws weakened this check.

First, the original principal was authorized with the proxy's authentication data instead of its own. On the admin REST API of the broker and the functions worker, this applied to every proxied request. On the Pulsar binary protocol, it applied when the proxy did not forward the client's credentials to the broker, which was the default of the Pulsar proxy in the affected versions. Authorization providers that resolve permissions from the role name only, such as the default authorization provider, are not affected by this flaw. The multi-role token authorization provider (MultiRolesTokenAuthorizationProvider), added in Apache Pulsar 2.8.1, resolves roles from the role claim of the token in the authentication data it is given. When a proxy authenticates to the broker with its own token, the original principal was therefore authorized with all roles in the proxy's token. If any of those roles is a superuser or tenant admin role, any user whose requests are forwarded by that proxy can perform operations that need those permissions without holding them. Custom authorization providers that use the authentication data could be affected in a similar way.

Second, independently of the authorization provider, the tenant admin check of a proxied admin REST API request succeeded without checking the original principal when the proxy role was itself an admin role of the tenant. In deployments where a proxy role is a tenant admin, including with the default authorization provider, any user whose requests are forwarded by that proxy could perform tenant administration operations on that tenant. This behavior is present from 2.8.4 in the 2.8.x releases, from 2.9.3 in the 2.9.x releases, and from 2.10.1 onwards.

Deployments that use neither the multi-role token authorization provider nor a custom provider that uses the authentication data are not affected by the first flaw, and with the multi-role token authorization provider, neither are deployments whose proxies do not authenticate to the broker with a token. Deployments in which no proxy role is listed as an admin role of a tenant are not affected by the second flaw. A proxy role that is a superuser but is not listed as a tenant admin does not trigger it, because the tenant admin check of the built-in authorization providers only considers the tenant's admin roles; this can differ for custom authorization providers that treat superusers as tenant admins.

In fixed versions, both the proxy role and the original principal are authorized for each proxied request, and the original principal is authorized only with its own authentication data. With the multi-role token authorization provider, the roles of a forwarded token are used for the original principal only when that token authenticates as the original principal; otherwise only the original principal's role name is used. For tenant admin checks, the proxy role and the original principal must each be a superuser or a tenant admin of the tenant.

This issue affects Apache Pulsar versions from 2.8.1 before 4.0.14 and from 4.1.0 before 4.2.5.

• 4.0.x version users should upgrade to at least 4.0.14.
• 4.1.x and 4.2.x version users should upgrade to at least 4.2.5.

Users operating versions prior to those listed above should upgrade to the aforementioned patched versions or newer versions.

The currently supported Apache Pulsar release lines are 4.0.x and 5.0.x. The supported versions schedule is available at https://pulsar.apache.org/contribute/release-policy/.

Affected

• apache_pulsar >= 2.8.1 < 4.0.14
• apache_pulsar >= 4.1.0 < 4.2.5

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.