CVE-2025-22021 netfilter: socket: Lookup orig tuple for IPv6 SNAT
Missing conntrack lookup in IPv6 SNAT causes transparent socket matching failures, potentially bypassing network policies in Kubernetes environments.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-22021?
CVE-2025-22021 is a critical vulnerability in Linux kernel, published on 16 Apr 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2025-22021?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-22021?
Apply the vendor's patch.
Is CVE-2025-22021 being exploited?
There is no known exploitation of CVE-2025-22021 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as DEBIAN-CVE-2025-22021, GHSA-57hq-w56x-2gq6, ROOT-OS-DEBIAN-12-CVE-2025-22021, ROOT-OS-UBUNTU-2404-CVE-2025-22021, UBUNTU-CVE-2025-22021.