---
title: "CVE-2026-79591: libxls - Use After Free"
description: "libxls 1.6.3 contains a heap-buffer-overflow and use-after-free vulnerability caused by insufficient validation of a file-controlled font index in xls_getCSS(), letting attackers cause memory corruption or code execution, exploit requires crafted file input."
url: https://panop.io/threat-heartbeat/CVE-2026-79591/
---

# CVE-2026-79591 libxls - Use After Free

libxls 1.6.3 contains a heap-buffer-overflow and use-after-free vulnerability caused by insufficient validation of a file-controlled font index in xls\_getCSS(), letting attackers cause memory corruption or code execution, exploit requires crafted file input.

CVSS base score 7.8 /10

High

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.17% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-79591)

## Details

Type

Use After Free

Impact

Remote Code Execution, Denial Of Service

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Published

10 September 2026

Updated

15 October 2026

Weakness

[CWE-122](https://cwe.mitre.org/data/definitions/122.html)

## Vendor fix

Update to the latest version of libxls.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-79591](https://nvd.nist.gov/vuln/detail/CVE-2026-79591)
- [https://github.com/libxls/libxls/issues/161](https://github.com/libxls/libxls/issues/161)
- [https://github.com/libxls/libxls/pull/164/changes/902c8f9b13710c3a13b6232fb86626c5c729402c](https://github.com/libxls/libxls/pull/164/changes/902c8f9b13710c3a13b6232fb86626c5c729402c)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

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