CVE-2020-21547Public exploitNetwork attack vector

Crash via high-color dithering buffer over-read

Published Sep 17, 2021 · Updated Aug 4, 2024

Heap-based buffer overflow in Libsixel 1.8.2 allows remote attackers to crash img2sixel through a crafted image processed in high-color mode. The high-color encoder fails to stop at the original image height before rewinding its pixel pointer, causing dither_func_fs to read past the allocated image buffer. A victim must pass the crafted image to img2sixel with --high-color; the published demonstration aborts an AddressSanitizer build, and no code execution is shown.

CVSS severity8.8
High
EPSS probability1.06%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap-based buffer overflow in Libsixel 1.8.2 allows remote attackers to crash img2sixel through a crafted image processed in high-color mode. The high-color encoder fails to stop at the original image height before rewinding its pixel pointer, causing dither_func_fs to read past the allocated image buffer. A victim must pass the crafted image to img2sixel with --high-color; the published demonstration aborts an AddressSanitizer build, and no code execution is shown.

The record

CVE
CVE-2020-21547
Published
Sep 17, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-787, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 17, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P
8.8Canonical UbuntuCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1203Exploitation for Client Execution

Public exploit references

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

Technologies

Your stack

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Your stack

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