A Allocation of Resources Without Limits or Throttling vulnerability in SUSE RKE2 allows attackers with access to K3s servers apiserver/supervisor port (TCP 6443) cause denial of service. This issue affects RKE2: from 1.24.0 before 1.24.17+rke2r1, from v1.25.0 before v1.25.13+rke2r1, from v1.26.0 before v1.26.8+rke2r1, from v1.27.0 before v1.27.5+rke2r1, from v1.28.0 before v1.28.1+rke2r1.

Affected: Go: github.com/rancher/rke2

### Impact

An issue was found in RKE2 where an attacker with network access to RKE2 servers' supervisor port (TCP 9345) can force the TLS server to add entries to the certificate's Subject Alternative Name (SAN) list, through a stuffing attack, until the certificate grows so large that it exceeds the maximum size allowed by TLS client implementations. OpenSSL for example will raise an `excessive message size` error when this occurs. No authentication is necessary to perform this attack, only the ability to perform a TLS handshake against the supervisor port (TCP 9345).

Affected servers will continue to operate, but clients (server or agent nodes) will fail to establish new connections when joining or rejoining the cluster, thus leading to a denial of service (DoS) attack.

### Remediation

Upgrade to a fixed release: - v1.28.1+rke2r1 - v1.27.5+rke2r1 - v1.26.8+rke2r1 - v1.25.13+rke2r1 - 1.24.17+rke2r1

If you are using RKE2 1.27 or earlier, you must also add the parameter `tls-san-security: true` to the RKE2 configuration to enable enhanced security for the supervisor's TLS SAN list. This option defaults to `true` starting with RKE2 1.28.

Note that this flag changes the behavior of RKE2's supervisor listener. You should ensure that you configure `node-external-ip` on servers that will be connected to via an external IP, and add `tls-san` entries for any load-balancers or VIP addresses that will be associated with the supervisor port. External IPs and load-balancer/VIP add…