# CVE-2023-4091: Samba: smb clients can truncate files with read-only permissions

> SMB clients can truncate read-only files when Samba is configured to ignore system ACLs, allowing unauthorized data modification.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 3 Nov 2023
- **Updated:** 20 Nov 2025
- **Also known as:** ALPINE-CVE-2023-4091, AZL-31900, AZL-37025, CLSA-2025-1738833923, CLSA-2026-1779132536, CLSA-2026-1779224622, DEBIAN-CVE-2023-4091, ECHO-21ee-19f3-8e74, GHSA-f6jj-3gjw-frjm, SUSE-SU-2023:4040-1, UBUNTU-CVE-2023-4091

## What is CVE-2023-4091?

CVE-2023-4091 is a medium-severity missing authorization vulnerability in Fedoraproject Fedora, published on 3 Nov 2023. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

A vulnerability was discovered in Samba, where the flaw allows SMB clients to truncate files, even with read-only permissions when the Samba VFS module "acl_xattr" is configured with "acl_xattr:ignore system acls = yes". The SMB protocol allows opening files when the client requests read-only access but then implicitly truncates the opened file to 0 bytes if the client specifies a separate OVERWRITE create disposition request. The issue arises in configurations that bypass kernel file system permissions checks, relying solely on Samba's permissions.

Weakness: CWE-276 (Incorrect Default Permissions)

## Which versions are affected by CVE-2023-4091?

It affects 5 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `samba` | SUSE:Linux Enterprise High Availability Extension 12 SP5 | All versions | 4.15.13+git.625.ac658f2f12-3.88.1 |
| `samba` | SUSE:Linux Enterprise Server 12 SP5 | All versions | 4.15.13+git.625.ac658f2f12-3.88.1 |
| `samba` | SUSE:Linux Enterprise Server for SAP Applications 12 SP5 | All versions | 4.15.13+git.625.ac658f2f12-3.88.1 |
| `samba` | SUSE:Linux Enterprise Software Development Kit 12 SP5 | All versions | 4.15.13+git.625.ac658f2f12-3.88.1 |

Products: Fedoraproject Fedora, Redhat Enterprise Linux, Redhat Enterprise Linux Eus, Redhat Storage, Samba Samba.

## How do I fix CVE-2023-4091?

Apply the vendor's patch.

## Is CVE-2023-4091 being exploited?

There is no known exploitation of CVE-2023-4091 in the wild and no public exploit code.

## Other vulnerabilities in Fedoraproject Fedora

- [CVE-2024-4577](https://insights.sbomify.com/CVE-2024-4577/): PHP-CGI OS Command Injection (critical 9.8, exploited in the wild)
- [CVE-2021-39226](https://insights.sbomify.com/CVE-2021-39226/): Grafana Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2019-5544](https://insights.sbomify.com/CVE-2019-5544/): VMware ESXi and Horizon DaaS OpenSLP Heap-Based Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2024-4947](https://insights.sbomify.com/CVE-2024-4947/): Google Chromium V8 Type Confusion (critical 9.6, exploited in the wild)
- [CVE-2024-4671](https://insights.sbomify.com/CVE-2024-4671/): Google Chromium Visuals Use-After-Free (critical 9.6, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-4091 and fix it if it is affected.

What it is: CVE-2023-4091 is a medium-severity missing authorization vulnerability in Fedoraproject Fedora, published on 3 Nov 2023. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-4091 in the wild and no public exploit code.

Affected product: Fedoraproject Fedora. 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-2023-4091/ (Markdown: https://insights.sbomify.com/CVE-2023-4091/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-4091
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-4091
- OSV: https://osv.dev/vulnerability/CVE-2023-4091

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-4091/
Summaries are generated and may contain mistakes; the official description above is the record.