CVE-2021-41715Public exploitNetwork attack vector

Application crash via double dither palette unref

Published Apr 8, 2022 · Updated Aug 4, 2024

Use after free in libsixel 1.10.0 allows attackers to crash img2sixel by inducing conversion of a crafted image. The failure path in sixel_encoder_prepare_palette frees the dither palette before sixel_encoder_encode_frame unrefs it again and reads freed memory in sixel_dither_unref. Exploitation requires user interaction to process the crafted file; the published proof of concept produces an AddressSanitizer abort, while further code execution was not demonstrated.

CVSS severity8.8
High
EPSS probability1.02%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use after free in libsixel 1.10.0 allows attackers to crash img2sixel by inducing conversion of a crafted image. The failure path in sixel_encoder_prepare_palette frees the dither palette before sixel_encoder_encode_frame unrefs it again and reads freed memory in sixel_dither_unref. Exploitation requires user interaction to process the crafted file; the published proof of concept produces an AddressSanitizer abort, while further code execution was not demonstrated.

The record

CVE
CVE-2021-41715
Published
Apr 8, 2022
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-416, T1204.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 8, 2022CVE 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

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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-416Use After Free
T1204.002Malicious File

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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