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Fencer Vulns
medium 5.5

CVE-2021-3566 json

Prior to ffmpeg version 4.3, the tty demuxer did not have a '`read_probe`' function assigned to it

published 2021-08-05 5 y ago modified 2026-07-23 3 mo ago also EUVD-2021-26876 , JLSEC-2025-116

cvss
5.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.9%
EPSS 0.9% chance of exploitation in 30 days, percentile 59%
public exploits
0
none known

Summary

Prior to ffmpeg version 4.3, the tty demuxer did not have a 'read_probe' function assigned to it. By crafting a legitimate "ffconcat" file that references an image, followed by a file the triggers the tty demuxer, the contents of the second file will be copied into the output file verbatim (as long as the `-vcodec copy` option is passed to ffmpeg).

Patch / fix

  • julia FFMPEG_jll 4.3.1+0
  • ffmpeg ffmpeg 4.3
  • ffmpeg Debian 14, Debian 13, Debian 12 7:4.3-2

debian advisories DEBIAN-CVE-2021-3566

  • ffmpeg Ubuntu Pro 16.04 LTS 7:2.8.17-0ubuntu0.1+esm4

ubuntu advisories UBUNTU-CVE-2021-3566

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • ffmpeg SLES for SAP 15 SP1, SLES for SAP 15, SLES 15-LTSS +7 more 3.4.2-150000.4.44.1
  • ffmpeg SLE Workstation Extension 15 SP3, SLE Workstation Extension 15 SP2, SLE Module for Package Hub 15 SP3 +3 more 3.4.2-11.17.1

suse advisories SUSE-SU-2023:0005-1SUSE-SU-2021:3521-1

  • ffmpeg openSUSE Leap 15.3 3.4.2-11.17.1

opensuse advisories openSUSE-SU-2021:3521-1

Exploit prediction

0.88% chance of exploitation in the next 30 days, higher than 59% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:P/I:N/A:N
OSV 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

Affected packages

ecosystem package affected fixed in
julia FFMPEG_jll
<4.3.1+0
4.3.1+0

Affected products

  • n/a ffmpeg

Classification

Weakness
  • CWE-200 Exposure of Sensitive Information to an Unauthorized Actor

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.