etcd: Watch API authorization bypass via open-ended range requests

Impact

What kind of vulnerability is it? Who is impacted?

A user granted READ permission on a single, exact key can use the Watch gRPC API with clientv3.WithFromKey() (an open-ended, "from this key to the end of the keyspace" watch) to receive watch events for every key lexicographically greater than or equal to their permitted key — not just the one key they were granted.

This is an authorization bypass in etcd's RBAC enforcement for the Watch API; Range/Get and DeleteRange requests are not affected. It only affects clusters with authentication enabled — clusters running without auth already allow unrestricted read access.

Patches

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

This vulnerability is patched in the following versions:

• etcd 3.7.1
• etcd 3.6.14
• etcd 3.5.33

Workarounds

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

If upgrading is not immediately possible, the following mitigations reduce exposure:

• Audit READ grants. Any READ grant — even on one key — can be leveraged via Watch to read everything after it. Review who holds READ permissions and revoke/tighten any you wouldn't trust with full read access.
• Restrict network access. Limit which hosts can reach etcd's client (gRPC) port via firewall rules or network policy, reducing who can attempt exploitation.

Reporter

• Luis Toro (@lobuhi on Github)
• Anthropic and Adam Korczynski (@AdamKorcz on Github)