CVE-2025-22021

In the Linux kernel, the following vulnerability has been resolved:

netfilter: socket: Lookup orig tuple for IPv6 SNAT

nf_sk_lookup_slow_v4 does the conntrack lookup for IPv4 packets to restore the original 5-tuple in case of SNAT, to be able to find the right socket (if any). Then socket_match() can correctly check whether the socket was transparent.

However, the IPv6 counterpart (nf_sk_lookup_slow_v6) lacks this conntrack lookup, making xt_socket fail to match on the socket when the packet was SNATed. Add the same logic to nf_sk_lookup_slow_v6.

IPv6 SNAT is used in Kubernetes clusters for pod-to-world packets, as pods' addresses are in the fd00::/8 ULA subnet and need to be replaced with the node's external address. Cilium leverages Envoy to enforce L7 policies, and Envoy uses transparent sockets. Cilium inserts an iptables prerouting rule that matches on -m socket --transparent and redirects the packets to localhost, but it fails to match SNATed IPv6 packets due to that missing conntrack lookup.

This vulnerability is rated as having a Moderate impact because it only manifests under specific networking topologies involving IPv6 source network address translation combined with transparent socket matching in netfilter. Standard Red Hat Enterprise Linux deployments do not utilize this combination by default, which restricts exposure primarily to specialized containerized environments using proxies that rely on transparent redirection. Because the issue results in improper socket matching and traffic redirection failure rather than remote code execution or arbitrary memory corruption, its blast radius is constrained to affected network flows.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.