{"id":"CVE-2025-68206","state":"PUBLISHED","title":"netfilter: nft_ct: add seqadj extension for natted connections","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: nft_ct: add seqadj extension for natted connections\n\nSequence adjustment may be required for FTP traffic with PASV/EPSV modes.\ndue to need to re-write packet payload (IP, port) on the ftp control\nconnection. This can require changes to the TCP length and expected\nseq / ack_seq.\n\nThe easiest way to reproduce this issue is with PASV mode.\nExample ruleset:\ntable inet ftp_nat {\n        ct helper ftp_helper {\n                type \"ftp\" protocol tcp\n                l3proto inet\n        }\n\n        chain prerouting {\n                type filter hook prerouting priority 0; policy accept;\n                tcp dport 21 ct state new ct helper set \"ftp_helper\"\n        }\n}\ntable ip nat {\n        chain prerouting {\n                type nat hook prerouting priority -100; policy accept;\n                tcp dport 21 dnat ip prefix to ip daddr map {\n\t\t\t192.168.100.1 : 192.168.13.2/32 }\n        }\n\n        chain postrouting {\n                type nat hook postrouting priority 100 ; policy accept;\n                tcp sport 21 snat ip prefix to ip saddr map {\n\t\t\t192.168.13.2 : 192.168.100.1/32 }\n        }\n}\n\nNote that the ftp helper gets assigned *after* the dnat setup.\n\nThe inverse (nat after helper assign) is handled by an existing\ncheck in nf_nat_setup_info() and will not show the problem.\n\nTopoloy:\n\n +-------------------+     +----------------------------------+\n | FTP: 192.168.13.2 | <-> | NAT: 192.168.13.3, 192.168.100.1 |\n +-------------------+     +----------------------------------+\n                                      |\n                         +-----------------------+\n                         | Client: 192.168.100.2 |\n                         +-----------------------+\n\nftp nat changes do not work as expected in this case:\nConnected to 192.168.100.1.\n[..]\nftp> epsv\nEPSV/EPRT on IPv4 off.\nftp> ls\n227 Entering passive mode (192,168,100,1,209,129).\n421 Service not available, remote server has closed connection.\n\nKernel logs:\nMissing nfct_seqadj_ext_add() setup call\nWARNING: CPU: 1 PID: 0 at net/netfilter/nf_conntrack_seqadj.c:41\n[..]\n __nf_nat_mangle_tcp_packet+0x100/0x160 [nf_nat]\n nf_nat_ftp+0x142/0x280 [nf_nat_ftp]\n help+0x4d1/0x880 [nf_conntrack_ftp]\n nf_confirm+0x122/0x2e0 [nf_conntrack]\n nf_hook_slow+0x3c/0xb0\n ..\n\nFix this by adding the required extension when a conntrack helper is assigned\nto a connection that has a nat binding.","publishedAt":"2025-12-16T13:48:33.763Z","updatedAt":"2026-10-15T22:02:47.582Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"1a64edf54f55d7956cf5a0d95898bc1f84f9b818","status":"affected","lessThan":"83273af0b60c093ba0085c205864d8542e1b1653","versionType":"git"},{"version":"1a64edf54f55d7956cf5a0d95898bc1f84f9b818","status":"affected","lessThan":"b19492c25eff04852e0cb58f9bb8238b6695ed2d","versionType":"git"},{"version":"1a64edf54f55d7956cf5a0d95898bc1f84f9b818","status":"affected","lessThan":"4de80f0dc3868408dd7fe9817e507123c9dd8bb0","versionType":"git"},{"version":"1a64edf54f55d7956cf5a0d95898bc1f84f9b818","status":"affected","lessThan":"b477ef7fa612fa45b6b3134d90d1eeb09396500a","versionType":"git"},{"version":"1a64edf54f55d7956cf5a0d95898bc1f84f9b818","status":"affected","lessThan":"4ab2cd906e4e1a19ddbda6eb532851b0e9cda110","versionType":"git"},{"version":"1a64edf54f55d7956cf5a0d95898bc1f84f9b818","status":"affected","lessThan":"2b52d89cbbb0dbe3e948d8d9a91e704316dccfe6","versionType":"git"},{"version":"1a64edf54f55d7956cf5a0d95898bc1f84f9b818","status":"affected","lessThan":"90918e3b6404c2a37837b8f11692471b4c512de2","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/netfilter/nft_ct.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.12","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.12","versionType":"semver"},{"version":"5.10.253","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.203","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.167","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.130","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.64","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.17.9","status":"unaffected","lessThanOrEqual":"6.17.*","versionType":"semver"},{"version":"6.18","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/netfilter/nft_ct.c"]}],"references":["https://git.kernel.org/stable/c/83273af0b60c093ba0085c205864d8542e1b1653","https://git.kernel.org/stable/c/b19492c25eff04852e0cb58f9bb8238b6695ed2d","https://git.kernel.org/stable/c/4de80f0dc3868408dd7fe9817e507123c9dd8bb0","https://git.kernel.org/stable/c/b477ef7fa612fa45b6b3134d90d1eeb09396500a","https://git.kernel.org/stable/c/4ab2cd906e4e1a19ddbda6eb532851b0e9cda110","https://git.kernel.org/stable/c/2b52d89cbbb0dbe3e948d8d9a91e704316dccfe6","https://git.kernel.org/stable/c/90918e3b6404c2a37837b8f11692471b4c512de2","https://cert-portal.siemens.com/productcert/html/ssa-082556.html","https://cert-portal.siemens.com/productcert/html/ssa-019113.html","https://cert-portal.siemens.com/productcert/html/ssa-457936.html","https://cert-portal.siemens.com/productcert/html/ssa-784472.html"],"weaknesses":[],"ingestedAt":"2026-10-29T20:09:56.034Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2025/68xxx/CVE-2025-68206.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2025-68206","state":"PUBLISHED","datePublished":"2025-12-16T13:48:33.763Z","dateUpdated":"2026-10-15T22:02:47.582Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2025-12-16T13:41:40.255Z"},"containers":{"cna":{"title":"netfilter: nft_ct: add seqadj extension for natted connections","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: nft_ct: add seqadj extension for natted connections\n\nSequence adjustment may be required for FTP traffic with PASV/EPSV modes.\ndue to need to re-write packet payload (IP, port) on the ftp control\nconnection. This can require changes to the TCP length and expected\nseq / ack_seq.\n\nThe easiest way to reproduce this issue is with PASV mode.\nExample ruleset:\ntable inet ftp_nat {\n        ct helper ftp_helper {\n                type \"ftp\" protocol tcp\n                l3proto inet\n        }\n\n        chain prerouting {\n                type filter hook prerouting priority 0; policy accept;\n                tcp dport 21 ct state new ct helper set \"ftp_helper\"\n        }\n}\ntable ip nat {\n        chain prerouting {\n                type nat hook prerouting priority -100; policy accept;\n                tcp dport 21 dnat ip prefix to ip daddr map {\n\t\t\t192.168.100.1 : 192.168.13.2/32 }\n        }\n\n        chain postrouting {\n                type nat hook postrouting priority 100 ; policy accept;\n                tcp sport 21 snat ip prefix to ip saddr map {\n\t\t\t192.168.13.2 : 192.168.100.1/32 }\n        }\n}\n\nNote that the ftp helper gets assigned *after* the dnat setup.\n\nThe inverse (nat after helper assign) is handled by an existing\ncheck in nf_nat_setup_info() and will not show the problem.\n\nTopoloy:\n\n +-------------------+     +----------------------------------+\n | FTP: 192.168.13.2 | <-> | NAT: 192.168.13.3, 192.168.100.1 |\n +-------------------+     +----------------------------------+\n                                      |\n                         +-----------------------+\n                         | Client: 192.168.100.2 |\n                         +-----------------------+\n\nftp nat changes do not work as expected in this case:\nConnected to 192.168.100.1.\n[..]\nftp> epsv\nEPSV/EPRT on IPv4 off.\nftp> ls\n227 Entering passive mode (192,168,100,1,209,129).\n421 Service not available, remote server has closed connection.\n\nKernel logs:\nMissing nfct_seqadj_ext_add() setup call\nWARNING: CPU: 1 PID: 0 at net/netfilter/nf_conntrack_seqadj.c:41\n[..]\n __nf_nat_mangle_tcp_packet+0x100/0x160 [nf_nat]\n nf_nat_ftp+0x142/0x280 [nf_nat_ftp]\n help+0x4d1/0x880 [nf_conntrack_ftp]\n nf_confirm+0x122/0x2e0 [nf_conntrack]\n nf_hook_slow+0x3c/0xb0\n ..\n\nFix this by adding the required extension when a conntrack helper is assigned\nto a connection that has a nat binding."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"1a64edf54f55d7956cf5a0d95898bc1f84f9b818","status":"affected","lessThan":"83273af0b60c093ba0085c205864d8542e1b1653","versionType":"git"},{"version":"1a64edf54f55d7956cf5a0d95898bc1f84f9b818","status":"affected","lessThan":"b19492c25eff04852e0cb58f9bb8238b6695ed2d","versionType":"git"},{"version":"1a64edf54f55d7956cf5a0d95898bc1f84f9b818","status":"affected","lessThan":"4de80f0dc3868408dd7fe9817e507123c9dd8bb0","versionType":"git"},{"version":"1a64edf54f55d7956cf5a0d95898bc1f84f9b818","status":"affected","lessThan":"b477ef7fa612fa45b6b3134d90d1eeb09396500a","versionType":"git"},{"version":"1a64edf54f55d7956cf5a0d95898bc1f84f9b818","status":"affected","lessThan":"4ab2cd906e4e1a19ddbda6eb532851b0e9cda110","versionType":"git"},{"version":"1a64edf54f55d7956cf5a0d95898bc1f84f9b818","status":"affected","lessThan":"2b52d89cbbb0dbe3e948d8d9a91e704316dccfe6","versionType":"git"},{"version":"1a64edf54f55d7956cf5a0d95898bc1f84f9b818","status":"affected","lessThan":"90918e3b6404c2a37837b8f11692471b4c512de2","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/netfilter/nft_ct.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.12","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.12","versionType":"semver"},{"version":"5.10.253","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.203","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.167","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.130","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.64","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.17.9","status":"unaffected","lessThanOrEqual":"6.17.*","versionType":"semver"},{"version":"6.18","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/netfilter/nft_ct.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/83273af0b60c093ba0085c205864d8542e1b1653"},{"url":"https://git.kernel.org/stable/c/b19492c25eff04852e0cb58f9bb8238b6695ed2d"},{"url":"https://git.kernel.org/stable/c/4de80f0dc3868408dd7fe9817e507123c9dd8bb0"},{"url":"https://git.kernel.org/stable/c/b477ef7fa612fa45b6b3134d90d1eeb09396500a"},{"url":"https://git.kernel.org/stable/c/4ab2cd906e4e1a19ddbda6eb532851b0e9cda110"},{"url":"https://git.kernel.org/stable/c/2b52d89cbbb0dbe3e948d8d9a91e704316dccfe6"},{"url":"https://git.kernel.org/stable/c/90918e3b6404c2a37837b8f11692471b4c512de2"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","baseScore":7.5,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:N - On an internet-facing gateway with the affected DNAT-before-helper rules, a remote FTP client can reach the path by requesting PASV/EPSV and causing the server reply to traverse netfilter.\nAC:L - Once the affected FTP NAT configuration exists, a length-changing payload rewrite triggers the flaw deterministically. No race, timing, or attacker-uncontrollable memory layout is required.\nPR:N - CAP_NET_ADMIN is required only for the operator to install the ruleset, not for exploitation. A remote client of an anonymous FTP service needs no account or kernel privilege.\nUI:N - No victim action is required after the FTP service and NAT rules are deployed; the network protocol exchange triggers the vulnerable path.\nS:U - The impact remains within the gateway's kernel and system security authority, without crossing a VM, IOMMU, or comparable boundary.\nC:N - The missing extension is detected before dereference, and the path performs no out-of-bounds read, stale-memory access, or information disclosure.\nI:N - There is no memory corruption or attacker-controlled write primitive. The intended FTP payload rewrite merely becomes TCP-sequence-desynchronized because its adjustment state is not recorded.\nA:H - The path reliably executes WARN_ONCE, which causes a complete kernel panic on reasonable panic_on_warn deployments. 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