# CVE-2021-47603: audit: improve robustness of the audit queue handling

> A local attacker with root privileges can cause a denial of service by stopping the audit daemon, leading to unbounded kernel queue growth and system hangs.

- **Severity:** Medium 4.4 (`CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Jun 2024
- **Updated:** 23 May 2026
- **Also known as:** DEBIAN-CVE-2021-47603, GHSA-xfpp-3cjf-2x3v, UBUNTU-CVE-2021-47603

## What is CVE-2021-47603?

CVE-2021-47603 is a medium-severity denial of service vulnerability in Linux kernel, published on 19 Jun 2024. 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:

audit: improve robustness of the audit queue handling

If the audit daemon were ever to get stuck in a stopped state the
kernel's kauditd_thread() could get blocked attempting to send audit
records to the userspace audit daemon.  With the kernel thread
blocked it is possible that the audit queue could grow unbounded as
certain audit record generating events must be exempt from the queue
limits else the system enter a deadlock state.

This patch resolves this problem by lowering the kernel thread's
socket sending timeout from MAX_SCHEDULE_TIMEOUT to HZ/10 and tweaks
the kauditd_send_queue() function to better manage the various audit
queues when connection problems occur between the kernel and the
audit daemon.  With this patch, the backlog may temporarily grow
beyond the defined limits when the audit daemon is stopped and the
system is under heavy audit pressure, but kauditd_thread() will
continue to make progress and drain the queues as it would for other
connection problems.  For example, with the audit daemon put into a
stopped state and the system configured to audit every syscall it
was still possible to shutdown the system without a kernel panic,
deadlock, etc.; granted, the system was slow to shutdown but that is
to be expected given the extreme pressure of recording every syscall.

The timeout value of HZ/10 was chosen primarily through
experimentation and this developer's "gut feeling".  There is likely
no one perfect value, but as this scenario is limited in scope (root
privileges would be needed to send SIGSTOP to the audit daemon), it
is likely not worth exposing this as a tunable at present.  This can
always be done at a later date if it proves necessary.

Weakness: CWE-667 (Improper Locking)

## Which versions are affected by CVE-2021-47603?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-47603?

Apply the vendor's patch.

## Is CVE-2021-47603 being exploited?

There is no known exploitation of CVE-2021-47603 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-2021-47603 and fix it if it is affected.

What it is: CVE-2021-47603 is a medium-severity denial of service vulnerability in Linux kernel, published on 19 Jun 2024. 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-2021-47603 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-2021-47603/ (Markdown: https://insights.sbomify.com/CVE-2021-47603/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47603
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47603
- OSV: https://osv.dev/vulnerability/CVE-2021-47603

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47603/
Summaries are generated and may contain mistakes; the official description above is the record.