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netfilter: nft_ct: add seqadj extension for natted connections

Type: advisorySources: OSV

In the Linux kernel, the following vulnerability has been resolved: netfilter: nft_ct: add seqadj extension for natted connections Sequence adjustment may be required for FTP traffic with PASV/EPSV modes. due to need to re-write packet payload (IP, port) on the ftp control connection. This can require changes to the TCP length and expected seq / ack_seq. The easiest way to reproduce this issue is with PASV mode. Example ruleset: table inet ftp_nat { ct helper ftp_helper { type "ftp" protocol tcp l3proto inet } chain prerouting { type filter hook prerouting priority 0; policy accept; tcp dport 21 ct state new ct helper set "ftp_helper" } } table ip nat { chain prerouting { type nat hook prerouting priority -100; policy accept; tcp dport 21 dnat ip prefix to ip daddr map { 192.168.100.1 : 192.168.13.2/32 } } chain postrouting { type nat hook postrouting priority 100 ; policy accept; tcp sport 21 snat ip prefix to ip saddr map { 192.168.13.2 : 192.168.100.1/32 } } } Note that the ftp helper gets assigned *after* the dnat setup. The inverse (nat after helper assign) is handled by an existing check in nf_nat_setup_info() and will not show the problem. Topoloy: +-------------------+ +----------------------------------+ | FTP: 192.168.13.2 | <-> | NAT: 192.168.13.3, 192.168.100.1 | +-------------------+ +----------------------------------+ | +-----------------------+ | Client: 192.168.100.2 | +-----------------------+ ftp nat changes do not work as expected in this case: Connected t

Products
Kernel
Affected versions
Not specified
Fixed versions
5.10.253, 5.15.203, 6.1.167, 6.12.64, 6.17.9, 6.6.130
CVEs
CVE-2025-68206
Confirmed fixed CVEs
Not specified
Updated in this feed
4 Nov 2026, 17:50 UTC · Revision 1

Source evidence

netfilter: nft_ct: add seqadj extension for natted connections

core-osv · Original source

Published 16 Dec 2025, 13:48 UTC

In the Linux kernel, the following vulnerability has been resolved: netfilter: nft_ct: add seqadj extension for natted connections Sequence adjustment may be required for FTP traffic with PASV/EPSV modes. due to need to re-write packet payload (IP, port) on the ftp control connection. This can require changes to the TCP length and expected seq / ack_seq. The easiest way to reproduce this issue is with PASV mode. Example ruleset: table inet ftp_nat { ct helper ftp_helper { type "ftp" protocol tcp l3proto inet } chain prerouting { type filter hook prerouting priority 0; policy accept; tcp dport 21 ct state new ct helper set "ftp_helper" } } table ip nat { chain prerouting { type nat hook prerouting priority -100; policy accept; tcp dport 21 dnat ip prefix to ip daddr map { 192.168.100.1 : 192.168.13.2/32 } } chain postrouting { type nat hook postrouting priority 100 ; policy accept; tcp sport 21 snat ip prefix to ip saddr map { 192.168.13.2 : 192.168.100.1/32 } } } Note that the ftp helper gets assigned *after* the dnat setup. The inverse (nat after helper assign) is handled by an existing check in nf_nat_setup_info() and will not show the problem. Topoloy: +-------------------+ +----------------------------------+ | FTP: 192.168.13.2 | <-> | NAT: 192.168.13.3, 192.168.100.1 | +-------------------+ +----------------------------------+ | +-----------------------+ | Client: 192.168.100.2 | +-----------------------+ ftp nat changes do not work as expected in this case: Connected t

osv:CVE-2025-68206

Kernel

Fixed versions: 5.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.64, 6.17.9

Complete source record
{
  "id": "27afa0e9484c81cbffa86625cf06e7d047dfc45ae4e0db57c7ecc0739a213cda",
  "url": "https://osv.dev/vulnerability/CVE-2025-68206",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "netfilter: nft_ct: add seqadj extension for natted connections",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: netfilter: nft_ct: add seqadj extension for natted connections Sequence adjustment may be required for FTP traffic with PASV/EPSV modes. due to need to re-write packet payload (IP, port) on the ftp control connection. This can require changes to the TCP length and expected seq / ack_seq. The easiest way to reproduce this issue is with PASV mode. Example ruleset: table inet ftp_nat { ct helper ftp_helper { type \"ftp\" protocol tcp l3proto inet } chain prerouting { type filter hook prerouting priority 0; policy accept; tcp dport 21 ct state new ct helper set \"ftp_helper\" } } table ip nat { chain prerouting { type nat hook prerouting priority -100; policy accept; tcp dport 21 dnat ip prefix to ip daddr map { 192.168.100.1 : 192.168.13.2/32 } } chain postrouting { type nat hook postrouting priority 100 ; policy accept; tcp sport 21 snat ip prefix to ip saddr map { 192.168.13.2 : 192.168.100.1/32 } } } Note that the ftp helper gets assigned *after* the dnat setup. The inverse (nat after helper assign) is handled by an existing check in nf_nat_setup_info() and will not show the problem. Topoloy: +-------------------+ +----------------------------------+ | FTP: 192.168.13.2 | <-> | NAT: 192.168.13.3, 192.168.100.1 | +-------------------+ +----------------------------------+ | +-----------------------+ | Client: 192.168.100.2 | +-----------------------+ ftp nat changes do not work as expected in this case: Connected t",
    "evidence": "osv:CVE-2025-68206",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
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            "value": "5.10.253",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "5.15.203",
            "evidence": "/affected/1/ranges"
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          {
            "value": "6.1.167",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.130",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.64",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.17.9",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2025-68206",
      "aliases": [
        "CVE-2025-68206"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
        }
      ],
      "affected": [
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              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
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                {
                  "fixed": "83273af0b60c093ba0085c205864d8542e1b1653"
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                {
                  "fixed": "b19492c25eff04852e0cb58f9bb8238b6695ed2d"
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                {
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                {
                  "fixed": "2b52d89cbbb0dbe3e948d8d9a91e704316dccfe6"
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                {
                  "fixed": "90918e3b6404c2a37837b8f11692471b4c512de2"
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              ]
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          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-68206.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "4.12.0"
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                {
                  "fixed": "5.10.253"
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
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                  "introduced": "5.11.0"
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              ]
            },
            {
              "type": "ECOSYSTEM",
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                {
                  "introduced": "6.13.0"
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          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
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          "database_specific": {
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        }
      ],
      "modified": "2026-10-28T02:30:38.278620264Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-019113.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-082556.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-457936.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-784472.html",
        "https://git.kernel.org/stable/c/2b52d89cbbb0dbe3e948d8d9a91e704316dccfe6",
        "https://git.kernel.org/stable/c/4ab2cd906e4e1a19ddbda6eb532851b0e9cda110",
        "https://git.kernel.org/stable/c/4de80f0dc3868408dd7fe9817e507123c9dd8bb0",
        "https://git.kernel.org/stable/c/83273af0b60c093ba0085c205864d8542e1b1653",
        "https://git.kernel.org/stable/c/90918e3b6404c2a37837b8f11692471b4c512de2",
        "https://git.kernel.org/stable/c/b19492c25eff04852e0cb58f9bb8238b6695ed2d",
        "https://git.kernel.org/stable/c/b477ef7fa612fa45b6b3134d90d1eeb09396500a",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/68xxx/CVE-2025-68206.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-68206",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/68xxx/CVE-2025-68206.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2025-68206",
        "evidence": "/id"
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    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 505480,
  "published_at": "2025-12-16T13:48:33.763+00:00"
}