# CVE-2026-45949: hwrng: core - use RCU and work_struct to fix race condition

> A race condition in the Linux kernel's hardware random number generator driver can lead to a use-after-free, potentially allowing code execution or denial of service.

- **Severity:** Medium 4.7 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 May 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-88494, BELL-CVE-2026-45949, DEBIAN-CVE-2026-45949, GHSA-f8m7-rc76-gphg, ROOT-OS-DEBIAN-11-CVE-2026-45949, ROOT-OS-DEBIAN-12-CVE-2026-45949, ROOT-OS-UBUNTU-2204-CVE-2026-45949, ROOT-OS-UBUNTU-2404-CVE-2026-45949, UBUNTU-CVE-2026-45949

## What is CVE-2026-45949?

CVE-2026-45949 is a medium-severity vulnerability in Linux kernel, published on 27 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

hwrng: core - use RCU and work_struct to fix race condition

Currently, hwrng_fill is not cleared until the hwrng_fillfn() thread
exits. Since hwrng_unregister() reads hwrng_fill outside the rng_mutex
lock, a concurrent hwrng_unregister() may call kthread_stop() again on
the same task.

Additionally, if hwrng_unregister() is called immediately after
hwrng_register(), the stopped thread may have never been executed. Thus,
hwrng_fill remains dirty even after hwrng_unregister() returns. In this
case, subsequent calls to hwrng_register() will fail to start new
threads, and hwrng_unregister() will call kthread_stop() on the same
freed task. In both cases, a use-after-free occurs:

refcount_t: addition on 0; use-after-free.
WARNING: ... at lib/refcount.c:25 refcount_warn_saturate+0xec/0x1c0
Call Trace:
 kthread_stop+0x181/0x360
 hwrng_unregister+0x288/0x380
 virtrng_remove+0xe3/0x200

This patch fixes the race by protecting the global hwrng_fill pointer
inside the rng_mutex lock, so that hwrng_fillfn() thread is stopped only
once, and calls to kthread_run() and kthread_stop() are serialized
with the lock held.

To avoid deadlock in hwrng_fillfn() while being stopped with the lock
held, we convert current_rng to RCU, so that get_current_rng() can read
current_rng without holding the lock. To remove the lock from put_rng(),
we also delay the actual cleanup into a work_struct.

Since get_current_rng() no longer returns ERR_PTR values, the IS_ERR()
checks are removed from its callers.

With hwrng_fill protected by the rng_mutex lock, hwrng_fillfn() can no
longer clear hwrng_fill itself. Therefore, if hwrng_fillfn() returns
directly after current_rng is dropped, kthread_stop() would be called on
a freed task_struct later. To fix this, hwrng_fillfn() calls schedule()
now to keep the task alive until being stopped. The kthread_stop() call
is also moved from hwrng_unregister() to drop_current_rng(), ensuring
kthread_stop() is called on all possible paths where current_rng becomes
NULL, so that the thread would not wait forever.

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-45949?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-45949?

Apply the vendor's patch.

## Is CVE-2026-45949 being exploited?

There is no known exploitation of CVE-2026-45949 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-45949 and fix it if it is affected.

What it is: CVE-2026-45949 is a medium-severity vulnerability in Linux kernel, published on 27 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-45949 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-45949/ (Markdown: https://insights.sbomify.com/CVE-2026-45949/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45949
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45949
- OSV: https://osv.dev/vulnerability/CVE-2026-45949

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-45949/
Summaries are generated and may contain mistakes; the official description above is the record.