CVE-2025-22021

netfilter: socket: Lookup orig tuple for IPv6 SNAT

Published Apr 16, 2025 CVSS 3.1 · 10 Critical EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Debian DLA Debian DLA DLA-4178-1 linux security update
Debian DLA Debian DLA DLA-4193-1 linux-6.1 security update
EUVD EUVD EUVD-2025-11372 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.
Ubuntu USN Ubuntu USN USN-7585-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7585-2 Linux kernel (FIPS) vulnerabilities
Ubuntu USN Ubuntu USN USN-7585-3 Linux kernel (FIPS) vulnerabilities
Ubuntu USN Ubuntu USN USN-7585-4 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-7585-5 Linux kernel (HWE) vulnerabilities
Ubuntu USN Ubuntu USN USN-7585-6 Linux kernel (BlueField) vulnerabilities
Ubuntu USN Ubuntu USN USN-7585-7 Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN Ubuntu USN USN-7591-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7591-2 Linux kernel (FIPS) vulnerabilities
Ubuntu USN Ubuntu USN USN-7591-3 Linux kernel (Real-time) vulnerabilities
Ubuntu USN Ubuntu USN USN-7591-4 Linux kernel (AWS) vulnerabilities
Ubuntu USN Ubuntu USN USN-7591-5 Linux kernel (Intel IoTG) vulnerabilities
Ubuntu USN Ubuntu USN USN-7591-6 Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN Ubuntu USN USN-7592-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7593-1 Linux kernel (HWE) vulnerabilities
Ubuntu USN Ubuntu USN USN-7594-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7594-2 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-7594-3 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7597-1 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-7597-2 Linux kernel (Azure FIPS) vulnerabilities
Ubuntu USN Ubuntu USN USN-7598-1 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-7602-1 Linux kernel (Xilinx ZynqMP) vulnerabilities
Ubuntu USN Ubuntu USN USN-7605-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7605-2 Linux kernel (Low Latency) vulnerabilities
Ubuntu USN Ubuntu USN USN-7606-1 Linux kernel (OEM) vulnerabilities
Ubuntu USN Ubuntu USN USN-7628-1 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-7640-1 Linux kernel (IoT) vulnerabilities
Ubuntu USN Ubuntu USN USN-7655-1 Linux kernel (Intel IoTG) vulnerabilities
Ubuntu USN Ubuntu USN USN-7835-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7835-2 Linux kernel (Real-time) vulnerabilities
Ubuntu USN Ubuntu USN USN-7835-3 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7835-4 Linux kernel (HWE) vulnerabilities
Ubuntu USN Ubuntu USN USN-7835-5 Linux kernel (Oracle) vulnerabilities
Ubuntu USN Ubuntu USN USN-7835-6 Linux kernel (AWS) vulnerabilities
Ubuntu USN Ubuntu USN USN-7887-1 Linux kernel (Raspberry Pi Real-time) vulnerabilities
Ubuntu USN Ubuntu USN USN-7887-2 Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN Ubuntu USN USN-7940-1 Linux kernel (Azure FIPS) vulnerabilities
Ubuntu USN Ubuntu USN USN-7940-2 Linux kernel (Azure, N-Series) vulnerabilities
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}

cvssV3_1

{'score': 10, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H'}

Type Values Removed Values Added
First Time appeared Linux
Linux linux Kernel
Weaknesses NVD-CWE-noinfo
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:6.14:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
Type Values Removed Values Added
Weaknesses CWE-20
Type Values Removed Values Added
References
Metrics threat_severity

None

cvssV3_1

{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}

threat_severity

Moderate

Type Values Removed Values Added
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.
Title netfilter: socket: Lookup orig tuple for IPv6 SNAT
References
Weaknesses

Sources

Status
PUBLISHED
Assigner
Linux
Published
Updated
Oct 15, 2026, 9:51 PM
Reserved
Dec 29, 2024, 8:45 AM
Status
Modified
Published
Apr 16, 2025, 11:15 AM
Modified
Oct 15, 2026, 10:18 PM
Severity
Moderate
Public date
Apr 16, 2025, 12:00 AM