CVE-2025-68206
- Source
- https://cve.org/CVERecord?id=CVE-2025-68206
- Import Source
- https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-68206.json
- JSON Data
- https://api.osv.dev/v1/vulns/CVE-2025-68206
- Downstream
- Published
- 2025-12-16T13:48:33.763Z
- Modified
- 2026-01-08T20:05:45.509428Z
- Summary
- netfilter: nft_ct: add seqadj extension for natted connections
- Details
-
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 ftpnat { ct helper ftphelper { 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 nfnatsetup_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 nfctseqadjextadd() setup call WARNING: CPU: 1 PID: 0 at net/netfilter/nfconntrackseqadj.c:41 [..] _nfnatmangletcppacket+0x100/0x160 [nfnat] nfnatftp+0x142/0x280 [nfnatftp] help+0x4d1/0x880 [nfconntrackftp] nfconfirm+0x122/0x2e0 [nfconntrack] nfhook_slow+0x3c/0xb0 ..
Fix this by adding the required extension when a conntrack helper is assigned to a connection that has a nat binding.
- Database specific
{ "cna_assigner": "Linux", "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/68xxx/CVE-2025-68206.json" }- References
-
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
- https://git.kernel.org/stable/c/2b52d89cbbb0dbe3e948d8d9a91e704316dccfe6
- https://git.kernel.org/stable/c/4ab2cd906e4e1a19ddbda6eb532851b0e9cda110
- https://git.kernel.org/stable/c/90918e3b6404c2a37837b8f11692471b4c512de2
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/68xxx/CVE-2025-68206.json
- https://nvd.nist.gov/vuln/detail/CVE-2025-68206
Affected packages
Git / git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
Affected ranges
- Type
- GIT
- Repo
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
- Events
-
Introduced1a64edf54f55d7956cf5a0d95898bc1f84f9b818Fixed4ab2cd906e4e1a19ddbda6eb532851b0e9cda110Fixed2b52d89cbbb0dbe3e948d8d9a91e704316dccfe6Fixed90918e3b6404c2a37837b8f11692471b4c512de2