CVE-2021-40656: libsixel before 1.10 is vulnerable to Buffer Overflow in libsixel/src/quant.c:867.

Q: How do I fix CVE-2021-40656?

libsixel: upgrade to 1.10.0. Exact commands for each OS are on this page.

Q: Is CVE-2021-40656 being exploited?

CVE-2021-40656 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-40656 affect?

CVE-2021-40656 affects libsixel. Severity is high (CVSS 8.8). libsixel before 1.10 is vulnerable to Buffer Overflow in libsixel/src/quant.c:867.

Q: How urgent is CVE-2021-40656?

Priority 52/100. High severity; Public exploit reference

This month

HIGH 8.8UPGRADE

CVE-2021-40656 is a high-severity flaw (CVSS 8.8) affecting libsixel. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

libsixel before 1.10 is vulnerable to Buffer Overflow in libsixel/src/quant.c:867.

Why this priority

High severity
Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	8.8 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	1.0% (top 37%)
CISA exploited list	No
Weakness	CWE-787
Published	2022-04-08
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: libsixel

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2022-04-08 16:15 UTCPublished CVE record published
2026-06-17 04:07 UTCUpdated Record last modified

libsixel libsixel UPGRADE

Affected: < 1.10.0

Fixed in: 1.10.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy libsixel || rpm -q libsixel || libsixel --version

2. UPGRADE to 1.10.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade libsixel

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade libsixel

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-40656?

libsixel: upgrade to 1.10.0. Exact commands for each OS are on this page.

Is CVE-2021-40656 being exploited?

CVE-2021-40656 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-40656 affect?

CVE-2021-40656 affects libsixel. Severity is high (CVSS 8.8). libsixel before 1.10 is vulnerable to Buffer Overflow in libsixel/src/quant.c:867.

How urgent is CVE-2021-40656?

Priority 52/100. High severity; Public exploit reference

Related CVEs

CVE-2026-44637 HIGH 7.1 UPGRADE libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel
CVE-2026-44636 HIGH 7.4 UPGRADE libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel
CVE-2026-44638 LOW 2.5 UPGRADE libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel
CVE-2026-33023 HIGH 7.8 UPGRADE libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel
CVE-2026-33021 HIGH 7.3 UPGRADE libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel

References

← Back to latest CVEs