etcd RBAC bypass allows unauthorized data access via PrevKv/lease attachment in nested transaction Put requests

Impact

What kind of vulnerability is it? Who is impacted?

A vulnerability in etcd allows read access via PrevKv, or lease attachment in Put requests within transaction operations, to bypass RBAC authorization checks. An authenticated user without sufficient read or lease-related permissions may be able to access unauthorized data or attach leases by invoking transaction operations with these features enabled.

Kubernetes does not rely on etcd’s built-in authentication and authorization. Instead, the API server handles authentication and authorization itself, so typical Kubernetes deployments are not affected.

Patches

Has the problem been patched? What versions should users upgrade to?

This vulnerability is patched in the following versions:

• etcd 3.6.11
• etcd 3.5.30
• etcd 3.4.44

Workarounds

Is there a way for users to fix or remediate the vulnerability without upgrading?

If upgrading is not immediately possible, reduce exposure by treating the affected
RPCs as unauthenticated in practice.

• restrict network access to etcd server ports so only trusted components can connect
• require strong client identity at the transport layer, such as mTLS with tightly scoped client certificate
  distribution

Reporters

Samy Ghannad (@SamyGhannad on Github) reported that read access via PrevKv in a Put request within etcd transactions bypassed RBAC authorization checks. Benjamin Wang (@ahrtr ) further analyzed that lease attachment in a Put request within etcd transactions also bypassed RBAC authorization checks