# CVE-2026-56391: GNU coreutils out-of-bounds read in uniq

Source: https://junglewise.ai/threats/cve-2026-56391-gnu-coreutils-out-of-bounds-read-in-uniq  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-24. Updated: 2026-07-24  
License: CC BY 4.0 with a link back

CVE-2026-56391 · Severity: info · CVSS 4.6 · Published 2026-07-24

A vulnerability exists in the 'uniq' utility of GNU coreutils, a fundamental set of tools used in Linux and Unix-like operating systems. When processing specially crafted text files using certain character-checking options, the tool may crash or inadvertently expose small amounts of system memory. This could lead to a service disruption or the leakage of sensitive information to a local user.

Technologies: [Gnu Coreutils](https://junglewise.ai/threats/technologies/coreutils). Vendors: [Gnu](https://junglewise.ai/threats/vendors/gnu).

## Quick answers

**Is CVE-2026-56391 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-56391 being exploited in the wild.

**How severe is CVE-2026-56391?** Informational severity, with a CVSS score of 4.6, published 24 July 2026.

**Which products and versions are affected?** Gnu Coreutils 9.5 through 9.11.

**Is there a fix for CVE-2026-56391?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-56391 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-56391?** Check whether you run Gnu Coreutils at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

An out-of-bounds read vulnerability exists in the 'uniq' utility of GNU coreutils within the find_field() function. The flaw is caused by the incorrect handling of multibyte characters when the -w (--check-chars) flag is active; the function fails to advance a pointer correctly while calculating character byte lengths, leading to an inflated length value. This value is subsequently passed to memcmp(), resulting in a read beyond the allocated buffer. An attacker can exploit this by providing crafted multibyte input, potentially causing a denial-of-service (crash) or disclosing adjacent heap memory. The issue is fixed in commit d64e35a8a4c0e4608321433e0d84d917e4e36371.

## Affected products

- GNU coreutils 9.5 through 9.11

## Timeline

- 2026-07-24: disclosed
- 2026-07-24: advisory

## References

- [https://cert.pl/en/posts/2026/07/CVE-2026-56391](https://cert.pl/en/posts/2026/07/CVE-2026-56391)
- [https://git.savannah.gnu.org/cgit/coreutils.git/](https://git.savannah.gnu.org/cgit/coreutils.git/)
- [https://git.savannah.gnu.org/cgit/coreutils.git/commit/?id=d64e35a8a4c0e4608321433e0d84d917e4e36371](https://git.savannah.gnu.org/cgit/coreutils.git/commit/?id=d64e35a8a4c0e4608321433e0d84d917e4e36371)

## Related threats

- [GNU coreutils heap buffer overflow in unexpand](https://junglewise.ai/threats/cve-2026-56392-gnu-coreutils-heap-buffer-overflow-in-unexpand)
- [GNU Coreutils heap buffer under-read in sort utility](https://junglewise.ai/threats/cve-2025-5278-gnu-coreutils-heap-buffer-under-read-in-sort-utility)