Change:
CVSS Rating: In typical clusters: medium (5.4) In clusters where API server insecure port has not been disabled: high (8.8) A security issue was discovered in which allows adjacent hosts to reach TCP and UDP services bound to running on the node or in the node's network namespace. For example, if a cluster administrator runs a TCP service on a node that listens on , because of this bug, that service would be potentially reachable by other hosts on the same LAN as the node, or by containers running on the same node as the service. If the example service on port required no additional authentication (because it assumed that only other localhost processes could reach it), then it could be vulnerable to attacks that make use of this bug. The Kubernetes API Server's default insecure port setting causes the API server to listen on where it will accept requests without authentication. Many Kubernetes installers explicitly disable the API Server's insecure port, but in clusters where it is not disabled, an attacker with access to another system on the same LAN or with control of a container running on the master may be able to reach the API server and execute arbitrary API requests on the cluster. This port is deprecated, and will be removed in Kubernetes v1.20. You may be vulnerable if: You are running a vulnerable version (see below) Your cluster nodes run in an environment where untrusted hosts share the same layer 2 domain (i.e. same LAN) as nodes Your cluster allows untrusted pods to run containers with (the Kubernetes default is to allow this capability). Your nodes (or hostnetwork pods) run any localhost-only services which do not require any further authentication. To list services that are potentially affected, run the following commands on nodes: - On a master node, an lsof entry like this indicates that the API server may be listening with an insecure port: kubelet/kube-proxy v1.18.0-1.18.3 kubelet/kube-proxy v1.17.0-1.17.6 kubelet/kube-proxy <=1.16.10 Prior to upgrading, this vulnerability can be mitigated by manually adding an iptables rule on nodes. This rule will reject traffic to 127.0.0.1 which does not originate on the node. Additionally, if your cluster does not already have the API Server insecure port disabled, we strongly suggest that you disable it. Add the following flag to your kubernetes API server command line: Packets on the wire with an IPv4 destination in the range 127.0.0.0/8 and a layer-2 destination MAC address of a node may indicate that an attack is targeting this vulnerability. Although the issue is caused by , the current fix for the issue is in (although future versions may have the fix in instead). We recommend updating both and to be sure the issue is addressed. The following versions contain the fix: kubelet/kube-proxy master - fixed by kubelet/kube-proxy v1.18.4+ - fixed by kubelet/kube-proxy v1.17.7+ - fixed by kubelet/kube-proxy v1.16.11+ - fixed by To upgrade, refer to the documentation: This issue was originally raised in issue which details how the sets which causes the system not to reject traffic to localhost which originates on other hosts. IPv6-only services that bind to a address are not affected. There may be additional attack vectors possible in addition to those fixed by and its cherry-picks. For those attacks to succeed, the target service would need to be UDP and the attack could only rely upon sending UDP datagrams since it wouldn't receive any replies. Finally, the target node would need to have reverse-path filtering disabled for an attack to have any effect. Work is ongoing to determine whether and how this issue should be fixed. See for up-to-date status on this issue. This vulnerability was reported by János Kövér, Ericsson with additional impacts reported by Rory McCune, NCC Group and Yuval Avrahami and Ariel Zelivansky, Palo Alto Networks. /area security /kind bug /committee product-security /sig network /sig node /area kubelet
For insecure port removal:
The original announcement contained an error. The announcement makes it sound like upgrading kube-proxy will address the issue, but that is incorrect. I have edited the issue summary to add the following paragraph in the "Fixed Versions" section: Additionally, I have changed the components in listed versions to say kubelet/kube-proxy instead of kube-proxy.
Could you add numerical CVSS scores to these? "High" is too vague, frequently varies from vendor to vendor. I can calculate a score from the vector myself, but adding the score would save us some work...
Edited. Also, the vector scores are clickable and will show the CVSS scores too.
To be clear, this is fixed in v1.18.4+, v1.17.7+, and v1.16.11+ correct?
Right. Sorry if the extra paragraph in "Fixed Versions" made that unclear.
Got it. Thank you!
So just to be sure, this wouldn't be a problem in an EKS cluster running in its own VPC, right? (assuming no untrusted hosts on the same VPC)
Are all the conditions listed under , a logical AND ?
Edit: after more testing, I think is indeed required
The attack can be done from any pod with (this is still K8S default), so you might not be safe. a more accurate title: "Node setting allows to bypass localhost boundary"
We believe that of the four conditions, you might be affected if (1 and (2 or 3) and 4) are true for your cluster. Sorry that it's not super clear from the text. Trying and failing to convey info concisely and with precision makes me glad that I'm in software, not law.
Isn't this broadly fixed by ? We're discussing better answers and options for deployment, too, but I am curious what the close-condition for this bug is?
I made a typo in the issue description saying that this is addressed by instead of . I'll edit it now. Sorry about that. Yes, this is mostly fixed by . I marked this as closed due to that PR fixing the majority of security issues caused by the setting. We can re-open if people think that we should address the remaining case that talks about.
Sorry, folks. I thought that this issue was already closed. Maybe that makes my response above to less confusing.
Yes, this being open was one of the major points of confusion for us. Appreciate the clarification
/label official-cve-feed (Related to )

Discussion:
} // In IPVS proxy mode, the following flags need to be set <del> const sysctlRouteLocalnet = "net/ipv4/conf/all/route_localnet" </del> const sysctlBridgeCallIPTables = "net/bridge/bridge-nf-call-iptables" const sysctlVSConnTrack = "net/ipv4/vs/conntrack" const sysctlConnReuse = "net/ipv4/vs/conn_reuse_mode"

nodePortAddresses []string, kernelHandler KernelHandler, ) (*Proxier, error) { <del> // Set the route_localnet sysctl we need for if err := utilproxy.EnsureSysctl(sysctl, sysctlRouteLocalnet, 1); err != nil { return nil, err } </del> // Proxy needs br_netfilter and bridge-nf-call-iptables=1 when containers // are connected to a Linux bridge (but not SDN bridges).  Until most // plugins handle this, log when config is missing