# CVE-2023-34256: Information disclosure in n/a

> An out-of-bounds read in the Linux kernel ext4 filesystem allows attackers with block device access to read sensitive memory.

- **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:** 31 May 2023
- **Updated:** 11 Mar 2025
- **Also known as:** AZL-27063, DEBIAN-CVE-2023-34256, GHSA-rj85-7vr5-qv74, UBUNTU-CVE-2023-34256

## What is CVE-2023-34256?

CVE-2023-34256 is a medium-severity vulnerability in Debian Debian Linux, published on 31 May 2023. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

An issue was discovered in the Linux kernel before 6.3.3. There is an out-of-bounds read in crc16 in lib/crc16.c when called from fs/ext4/super.c because ext4_group_desc_csum does not properly check an offset. NOTE: this is disputed by third parties because the kernel is not intended to defend against attackers with the stated "When modifying the block device while it is mounted by the filesystem" access.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2023-34256?

It affects 3 products.


Products: Debian Debian Linux, Linux kernel, Suse Linux Enterprise.

## How do I fix CVE-2023-34256?

Apply the vendor's patch.

## Is CVE-2023-34256 being exploited?

There is no known exploitation of CVE-2023-34256 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-34256 and fix it if it is affected.

What it is: CVE-2023-34256 is a medium-severity vulnerability in Debian Debian Linux, published on 31 May 2023. 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-2023-34256 in the wild and no public exploit code.

Affected product: Debian Debian Linux. 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-2023-34256/ (Markdown: https://insights.sbomify.com/CVE-2023-34256/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-34256
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-34256
- OSV: https://osv.dev/vulnerability/CVE-2023-34256

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-34256/
Summaries are generated and may contain mistakes; the official description above is the record.