CVE-2026-33021: libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel

Q: How do I fix CVE-2026-33021?

libsixel: upgrade to 1.8.7-r1. Exact commands for each OS are on this page.

Q: Is CVE-2026-33021 being exploited?

CVE-2026-33021 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-2026-33021 affect?

CVE-2026-33021 affects libsixel. Severity is high (CVSS 7.3). libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. Versions 1.8.7 and prior contain a use-after-free vulnerability in sixel_encoder_encode_bytes() because sixel_frame_init() stores the caller-owned pixel buffer p

Q: How urgent is CVE-2026-33021?

Priority 35/100. High severity; Public exploit reference

Routine

HIGH 7.3UPGRADE

CVE-2026-33021 is a high-severity flaw (CVSS 7.3) affecting libsixel. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. Versions 1.8.7 and prior contain a use-after-free vulnerability in sixel_encoder_encode_bytes() because sixel_frame_init() stores the caller-owned pixel buffer pointer directly in frame->pixels without making a defensive copy. When a resize operation is triggered, sixel_frame_convert_to_rgb888() unconditionally frees this caller-owned buffer and replaces it with a new

Why this priority

High severity
Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	7.3 (High)
Attack vector	Local
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.2% (top 84%)
CISA exploited list	No
Weakness	CWE-416
Published	2026-04-14
Last modified	2026-07-25

Publisher (CNA): GitHub, Inc. · Vendor: saitoha

Last updated 2026-07-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-14 23:16 UTCPublished CVE record published
2026-07-25 11:10 UTCUpdated Record last modified

saitoha libsixel UPGRADE

Affected: < 1.8.7-r1

Fixed in: 1.8.7-r1

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 1.8.7-r1 (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-2026-33021?

libsixel: upgrade to 1.8.7-r1. Exact commands for each OS are on this page.

Is CVE-2026-33021 being exploited?

CVE-2026-33021 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-2026-33021 affect?

CVE-2026-33021 affects libsixel. Severity is high (CVSS 7.3). libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. Versions 1.8.7 and prior contain a use-after-free vulnerability in sixel_encoder_encode_bytes() because sixel_frame_init() stores the caller-owned pixel buffer p

How urgent is CVE-2026-33021?

Priority 35/100. 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-2026-33020 HIGH 7.1 UPGRADE libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel

References

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