CVE-2021-3566

Local file disclosure via unvalidated TTY probing

Published Aug 5, 2021 · Updated Aug 3, 2024

Information exposure in FFmpeg before 4.3 allows attackers to copy a referenced local file into output through a crafted ffconcat input. The concat demuxer can pass a referenced file to the TTY demuxer, whose missing read_probe accepts the file by extension and emits its bytes under stream copy. Processing the playlist with -vcodec copy and access to the referenced path is required; the consequence is disclosure of that file's contents.

CVSS severity5.5
Medium
EPSS probability0.88%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information exposure in FFmpeg before 4.3 allows attackers to copy a referenced local file into output through a crafted ffconcat input. The concat demuxer can pass a referenced file to the TTY demuxer, whose missing read_probe accepts the file by extension and emits its bytes under stream copy. Processing the playlist with -vcodec copy and access to the referenced path is required; the consequence is disclosure of that file's contents.

The record

CVE
CVE-2021-3566
Published
Aug 5, 2021
Updated
Aug 3, 2024
Vendor
FFmpeg
Product
FFmpeg
Classifications
CWE-200, T1005
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 5, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=ffmpeg 4.3

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

FFmpeg · FFmpegversion=ffmpeg 4.3

Published CVSS scores

5.5NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
4.3NVDAV:N/AC:M/Au:N/C:P/I:N/A:N

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)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-200Exposure of Sensitive Information to an Unauthorized Actor
T1005Data from Local System

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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