CVE-2020-21677

MEDIUMNVD 6.56.5—

6.5

A heap-based buffer overflow in the sixel_encoder_output_without_macro function in encoder.c of Libsixel 1.8.4 allows attackers to cause a denial of service (DOS) via converting a crafted PNG file into Sixel format.

CVSS v3: 6.5
EG Score: 6.5(medium)
EPSS: 51.5%
KEV: Not listed

Published

August 10, 2021

Last Modified

April 24, 2026

References (2)

cve@mitrehttps://github.com/saitoha/libsixel/issues/123
af854a3a-2127-422b-91ae-364da2661108https://github.com/saitoha/libsixel/issues/123

Weakness Classification(1)

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

CWE-787Out-of-bounds Write

Data Freshness Timeline

(refreshed 13× 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 13:45 UTCEPSS rescore
2026-06-06 13:45 UTCEPSS rescore
2026-06-05 22:45 UTCEPSS rescore
2026-06-05 22:45 UTCEPSS rescore
2026-06-05 10:00 UTCOSV refresh
2026-06-05 06:08 UTCEPSS rescore
2026-06-05 06:08 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

Frequently asked(5)

What is CVE-2020-21677?

CVE-2020-21677 is a medium vulnerability published on August 10, 2021. A heap-based buffer overflow in the sixelencoderoutputwithoutmacro function in encoder.c of Libsixel 1.8.4 allows attackers to cause a denial of service (DOS) via converting a crafted PNG file into Sixel format.

When was CVE-2020-21677 disclosed?

CVE-2020-21677 was first published in the National Vulnerability Database on August 10, 2021, 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-2020-21677 actively exploited?

CVE-2020-21677 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 51.5% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.

What is the CVSS score of CVE-2020-21677?

CVE-2020-21677 has a CVSS v3 base score of 6.5 (NVD).

How do I remediate CVE-2020-21677?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2020-21677, 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.

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CVE-2020-21677

📅 Published

🔄 Last Modified

🔗 References (2)

Weakness Classification(1)

Data Freshness Timeline

❓ Frequently asked(5)

Dependency Blast Radius

Is Your Infrastructure Affected by CVE-2020-21677?

🔗 Related CVEs(same CWE)

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Published

Last Modified

References (2)

Frequently asked(5)

Related CVEs(same CWE)