CVE-2020-21041Network attack vector

Process crash via unsupported monowhite APNG frames

Published May 24, 2021 · Updated Aug 4, 2024

Buffer overflow in the APNG encoder of FFmpeg 4.1 allows remote attackers to crash an encoding process with monowhite frame data. The encoder advertises AV_PIX_FMT_MONOBLACK even though apng_do_inverse_blend does not support it, allowing the routine to overrun a frame buffer. No authentication or user interaction is required, but an application must pass attacker-controlled monowhite frames to the APNG encoding path.

CVSS severity7.5
High
EPSS probability2.07%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overflow in the APNG encoder of FFmpeg 4.1 allows remote attackers to crash an encoding process with monowhite frame data. The encoder advertises AV_PIX_FMT_MONOBLACK even though apng_do_inverse_blend does not support it, allowing the routine to overrun a frame buffer. No authentication or user interaction is required, but an application must pass attacker-controlled monowhite frames to the APNG encoding path.

The record

CVE
CVE-2020-21041
Published
May 24, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-120, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 24, 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

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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.

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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 exploitUnconfirmed

Weakness, pattern, technique

CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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