---
id: CVE-2026-79591
title: >-
  A heap-buffer-overflow and use-after-free vulnerability exists in the
  xls_getCSS() function of libxls 1.6.3 due to insufficient validation of a
  file-controlled font index.
summary: >-
  A heap-buffer-overflow and use-after-free vulnerability exists in the
  xls_getCSS() function of libxls 1.6.3 due to insufficient validation of a
  file-controlled font index.
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H'
cwe:
  - CWE-122
published: '2026-09-10'
updated: '2026-09-22'
sourceUpdated: '2026-09-22T20:00:03.713'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-79591'
references:
  - url: 'https://github.com/libxls/libxls/issues/161'
    label: cve@mitre.org
  - url: >-
      https://github.com/libxls/libxls/pull/164/changes/902c8f9b13710c3a13b6232fb86626c5c729402c
    label: cve@mitre.org
  - url: 'https://github.com/libxls/libxls/issues/161'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
  - cve.org
  - exploit-available
epss: 0.00127
epssPercentile: 0.02673
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-09-15T14:09:00.571356Z'
ingestedAt: '2026-09-11T16:45:48.024Z'
---

## Overview

A heap-buffer-overflow and use-after-free vulnerability exists in the xls_getCSS() function of libxls 1.6.3 due to insufficient validation of a file-controlled font index.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.