# CVE-2026-56391: Out‑of‑bounds Read in GNU coreutils

> An out-of-bounds read in GNU coreutils uniq allows attackers to cause crashes or expose heap memory via crafted multibyte input.

- **Severity:** Medium 4.6 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 24 Jul 2026
- **Updated:** 24 Jul 2026
- **Also known as:** DEBIAN-CVE-2026-56391, ECHO-3699-27c7-123e, GHSA-7xvj-m9x7-qgxq, JLSEC-2026-1195, MGASA-2026-0439, RHSA-2026:46515, SUSE-SU-2026:24268-1, UBUNTU-CVE-2026-56391, openSUSE-SU-2026:22147-1

## What is CVE-2026-56391?

CVE-2026-56391 is a medium-severity memory corruption vulnerability in GNU coreutils, published on 24 Jul 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

GNU coreutils uniq is vulnerable to an out‑of‑bounds read due to incorrect handling of multibyte input when the -w (--check-chars) option is used. The find_field() function miscalculates the byte length of characters by repeatedly processing a fixed pointer instead of advancing through the input, resulting in an inflated length value. 
This incorrect length is later used in a memcmp operation, causing reads beyond the allocated buffer when processing crafted multibyte input.

When running GNU coreutils uniq with attacker-provided arguments, this behavior leads to a crash and potential adjacent heap memory exposure.

This issue has been fixed in the commit d64e35a8a4c0e4608321433e0d84d917e4e36371.

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

## Which versions are affected by CVE-2026-56391?

It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `coreutils` | Red Hat:hummingbird:1 | All versions | 0:9.11-5.1.hum1 |
| `coreutils-common` | Red Hat:hummingbird:1 | All versions | 0:9.11-5.1.hum1 |
| `coreutils-single` | Red Hat:hummingbird:1 | All versions | 0:9.11-5.1.hum1 |
| `coreutils` | SUSE:Linux Enterprise Server 16.0 | All versions | 9.6-160000.3.1 |
| `coreutils-single` | SUSE:Linux Enterprise Server 16.0 | All versions | 9.6-160000.3.1 |
| `coreutils-systemd` | SUSE:Linux Enterprise Server 16.0 | All versions | 9.6-160000.3.1 |
| `coreutils` | SUSE:Linux Enterprise Server for SAP applications 16.0 | All versions | 9.6-160000.3.1 |
| `coreutils-single` | SUSE:Linux Enterprise Server for SAP applications 16.0 | All versions | 9.6-160000.3.1 |
| `coreutils-systemd` | SUSE:Linux Enterprise Server for SAP applications 16.0 | All versions | 9.6-160000.3.1 |
| `coreutils` | openSUSE:Leap 16.0 | All versions | 9.6-160000.3.1 |
| `coreutils-single` | openSUSE:Leap 16.0 | All versions | 9.6-160000.3.1 |
| `coreutils-systemd` | openSUSE:Leap 16.0 | All versions | 9.6-160000.3.1 |
| `coreutils-testsuite` | openSUSE:Leap 16.0 | All versions | 9.6-160000.3.1 |

Products: Gnu Coreutils.

## How do I fix CVE-2026-56391?

Apply the vendor's patch.

## Is CVE-2026-56391 being exploited?

There is no known exploitation of CVE-2026-56391 in the wild and no public exploit code.

## Other vulnerabilities in GNU coreutils

- [CVE-2015-4042](https://insights.sbomify.com/CVE-2015-4042/): Integer overflow in n/a (critical 9.8)
- [CVE-2015-4041](https://insights.sbomify.com/CVE-2015-4041/): Memory corruption in n/a (high 7.8)
- [CVE-2017-18018](https://insights.sbomify.com/CVE-2017-18018/): Race condition in n/a (high 7.1)
- [CVE-2024-0684](https://insights.sbomify.com/CVE-2024-0684/): Coreutils: heap overflow in split --line-bytes with very long lines (medium 5.5)
- [CVE-2015-1865](https://insights.sbomify.com/CVE-2015-1865/): Race condition in n/a (medium 5.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-56391 and fix it if it is affected.

What it is: CVE-2026-56391 is a medium-severity memory corruption vulnerability in GNU coreutils, published on 24 Jul 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-56391 in the wild and no public exploit code.

Affected product: GNU coreutils. 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-2026-56391/ (Markdown: https://insights.sbomify.com/CVE-2026-56391/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-56391
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-56391
- OSV: https://osv.dev/vulnerability/CVE-2026-56391

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-56391/
Summaries are generated and may contain mistakes; the official description above is the record.