# CVE-2023-53421: blk-cgroup: Reinit blkg_iostat_set after clearing in blkcg_reset_stats()

> A missing re-initialization in the Linux kernel block cgroup code can cause a NULL pointer dereference, leading to a kernel panic and denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/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:** 18 Sep 2025
- **Updated:** 1 Jun 2026
- **Also known as:** AZL-71915, BELL-CVE-2023-53421, DEBIAN-CVE-2023-53421, GHSA-63xc-pmjj-q4vj, ROOT-OS-DEBIAN-11-CVE-2023-53421, ROOT-OS-DEBIAN-12-CVE-2023-53421, ROOT-OS-UBUNTU-2204-CVE-2023-53421, UBUNTU-CVE-2023-53421

## What is CVE-2023-53421?

CVE-2023-53421 is a medium-severity vulnerability in Linux kernel, published on 18 Sep 2025. 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:

blk-cgroup: Reinit blkg_iostat_set after clearing in blkcg_reset_stats()

When blkg_alloc() is called to allocate a blkcg_gq structure
with the associated blkg_iostat_set's, there are 2 fields within
blkg_iostat_set that requires proper initialization - blkg & sync.
The former field was introduced by commit 3b8cc6298724 ("blk-cgroup:
Optimize blkcg_rstat_flush()") while the later one was introduced by
commit f73316482977 ("blk-cgroup: reimplement basic IO stats using
cgroup rstat").

Unfortunately those fields in the blkg_iostat_set's are not properly
re-initialized when they are cleared in v1's blkcg_reset_stats(). This
can lead to a kernel panic due to NULL pointer access of the blkg
pointer. The missing initialization of sync is less problematic and
can be a problem in a debug kernel due to missing lockdep initialization.

Fix these problems by re-initializing them after memory clearing.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2023-53421?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2023-53421?

Apply the vendor's patch.

## Is CVE-2023-53421 being exploited?

There is no known exploitation of CVE-2023-53421 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-2023-53421 and fix it if it is affected.

What it is: CVE-2023-53421 is a medium-severity vulnerability in Linux kernel, published on 18 Sep 2025. 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-2023-53421 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-2023-53421/ (Markdown: https://insights.sbomify.com/CVE-2023-53421/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-53421
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-53421
- OSV: https://osv.dev/vulnerability/CVE-2023-53421

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-53421/
Summaries are generated and may contain mistakes; the official description above is the record.