CVE-2025-22021: Linux kernel · netfilter: socket: Lookup orig tuple for IPv6 SNAT
Source GCVE Database
Not known to be exploited · CVSS 5.5 Medium.
Data as of 29 Oct 2026, 22:52 UTC
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:HExploitation evidence
Disclosed: evidence found.
CVE published 16 Apr 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.
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.
References
- nvd.nist.gov/vuln/detail/CVE-2025-22021 (opens in a new tab)
- git.kernel.org/stable/c/1ca2169cc19dca893c7aae6af122852097435d16 (opens in a new tab)
- git.kernel.org/stable/c/1ec43100f7123010730b7ddfc3d5c2eac19e70e7 (opens in a new tab)
- git.kernel.org/stable/c/221c27259324ec1404f028d4f5a0f2ae7f63ee23 (opens in a new tab)
- git.kernel.org/stable/c/2bb139e483f8cbe488d19d8c1135ac3615e2668c (opens in a new tab)
- git.kernel.org/stable/c/41904cbb343d115931d6bf79aa2c815cac4ef72b (opens in a new tab)
- git.kernel.org/stable/c/5251041573850e5020cd447374e23010be698898 (opens in a new tab)
- git.kernel.org/stable/c/58ab63d3ded2ca6141357a2b24eee8453d0f871d (opens in a new tab)
- git.kernel.org/stable/c/6488b96a79a26e19100ad872622f04e93b638d7f (opens in a new tab)
- git.kernel.org/stable/c/932b32ffd7604fb00b5c57e239a3cc4d901ccf6e (opens in a new tab)
- lists.debian.org/debian-lts-announce/2025/05/msg00030.html (opens in a new tab)
- lists.debian.org/debian-lts-announce/2025/05/msg00045.html (opens in a new tab)