CVE-2026-79591

Memory corruption via unchecked font index

Published Sep 10, 2026 · Updated Sep 10, 2026

Heap-buffer overflow and use-after-free in libxls 1.6.3 allow attackers to corrupt memory by processing a crafted XLS file. xls_getCSS accepts a file-controlled font index without sufficient validation, causing out-of-bounds heap access and stale-pointer use. The flaw is reached when an application parses an untrusted XLS file; the published record establishes memory corruption but no more specific consequence.

CVSS severityUnavailable
Unscored
EPSS probability0.13%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Heap-buffer overflow and use-after-free in libxls 1.6.3 allow attackers to corrupt memory by processing a crafted XLS file. xls_getCSS accepts a file-controlled font index without sufficient validation, causing out-of-bounds heap access and stale-pointer use. The flaw is reached when an application parses an untrusted XLS file; the published record establishes memory corruption but no more specific consequence.

The record

CVE
CVE-2026-79591
Published
Sep 10, 2026
Updated
Sep 10, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1203
Attack vector
Unavailable
Privileges
Unavailable

Timeline

How it unfolded

  1. Sep 10, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 10, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorUnavailable in this record.
Required privilegesUnavailable in this record.

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

No CVSS assessment is available in this record.

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
VectorUnavailable
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo