CVE-2021-40656

HIGHNVD 8.88.8—

8.8

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

CVSS v3: 8.8
EG Score: 8.8(medium)
EPSS: 57.9%
KEV: Not listed

Published

April 8, 2022

Last Modified

April 24, 2026

Advisory Details (1)

Auto-updated May 2, 2026

No patch confirmed yet.

generic

heap-buffer-overflow in libsixel/src/quant.c:867 · Issue #25 · libsixel/libsixel · GitHub

https://github.com/libsixel/libsixel/issues/25

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

CWE-787Out-of-bounds Write

Data Freshness Timeline

(refreshed 12× in last 7d / 20× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

2026-06-08 14:15 UTCEPSS rescore
2026-06-08 14:15 UTCEPSS rescore
2026-06-07 15:23 UTCEPSS rescore
2026-06-07 15:23 UTCEPSS rescore
2026-06-06 13:46 UTCEPSS rescore
2026-06-06 13:46 UTCEPSS rescore
2026-06-05 22:45 UTCEPSS rescore
2026-06-05 10:00 UTCOSV refresh
2026-06-05 06:09 UTCEPSS rescore
2026-06-05 06:09 UTCEPSS rescore
2026-06-04 13:10 UTCEPSS rescore
2026-06-04 13:10 UTCEPSS rescore
2026-06-02 20:11 UTCEPSS rescore
2026-06-02 20:11 UTCEPSS rescore
2026-06-01 13:50 UTCEPSS rescore
2026-06-01 13:50 UTCEPSS rescore
2026-05-31 22:29 UTCEPSS rescore
2026-05-31 22:29 UTCEPSS rescore
2026-05-31 00:15 UTCEPSS rescore
2026-05-31 00:15 UTCEPSS rescore

Frequently asked(5)

What is CVE-2021-40656?

CVE-2021-40656 is a high vulnerability published on April 8, 2022. libsixel before 1.10 is vulnerable to Buffer Overflow in libsixel/src/quant.c:867.

When was CVE-2021-40656 disclosed?

CVE-2021-40656 was first published in the National Vulnerability Database on April 8, 2022, with the most recent update on April 24, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.

Is CVE-2021-40656 actively exploited?

CVE-2021-40656 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 57.9% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.

What is the CVSS score of CVE-2021-40656?

CVE-2021-40656 has a CVSS v3 base score of 8.8 (NVD).

How do I remediate CVE-2021-40656?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-40656, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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CVE-2021-40656

📅 Published

🔄 Last Modified

📋 Advisory Details (1)

heap-buffer-overflow in libsixel/src/quant.c:867 · Issue #25 · libsixel/libsixel · GitHub

Weakness Classification(1)

Data Freshness Timeline

❓ Frequently asked(5)

Dependency Blast Radius

Is Your Infrastructure Affected by CVE-2021-40656?

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Advisory Details (1)

Frequently asked(5)

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