CVE-2021-38171

CRITICALNVD 9.89.8—
EchelonGraph scoreMEDIUM confidence

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2022-05-24. NVD baseline CVSS 9.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
9.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 2%CVSS: 9.8Exploit: None knownExposed: 0

A fix is available — apply it.

adts_decode_extradata in libavformat/adtsenc.c in FFmpeg 4.4 does not check the init_get_bits return value, which is a necessary step because the second argument to init_get_bits can be crafted.

CVSS v3
9.8
EG Score
9.8(medium)
EG Risk
50(Track)
EG Risk 50/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity98% × 45%
Exploitation2% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
2%
EPSS %ILE
83%
KEV
Not listed

Published

August 21, 2021

Last Modified

November 21, 2024

Advisory Details (6)

Auto-updated Aug 21, 2026
Patch available. Sources: github_commit.
generic

FFmpeg: Multiple Vulnerabilities (GLSA 202312-14) — Gentoo security

https://security.gentoo.org/glsa/202312-14
generic

[FFmpeg-devel,v2,1/1] return value check for init_get_bits in adts_decode_extradata - Patchwork

https://patchwork.ffmpeg.org/project/ffmpeg/patch/AS8P193MB12542A86E22F8207EC971930B6F19%40AS8P193MB1254.EURP193.PROD.OUTLOOK.COM/
generic Patch Available

[SECURITY] [DLA 2818-1] ffmpeg security update

https://lists.debian.org/debian-lts-announce/2021/11/msg00012.html
github_commit

commit 9ffa49496d1a (FFmpeg/FFmpeg)

Fix landed in FFmpeg/FFmpeg commit 9ffa49496d1a — awaiting tagged release

https://github.com/FFmpeg/FFmpeg/commit/9ffa49496d1aae4cbbb387aac28a9e061a6ab0a6
generic

[SECURITY] [DSA 4998-1] ffmpeg security update

https://www.debian.org/security/2021/dsa-4998
generic

[SECURITY] [DSA 4990-1] ffmpeg security update

https://www.debian.org/security/2021/dsa-4990

Patch Availability(2)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntulibavdevice-dev (7:4.4.2-0ubuntu0.22.04.1) @ jammy2026-05-26ubuntu
ubuntulibavdevice-ffmpeg56 (7:2.8.17-0ubuntu0.1+esm4) @ xenial2026-05-26ubuntu

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(6 across 6 ecosystems)
Debian:10(1)
PackageVulnerable rangeFixed inDependents
ffmpeg7:4.1.3-1, 7:4.1.4-1, 7:4.1.4-1~deb10u1, 7:4.1.6-1~deb10u17:4.1.8-0+deb10u1—
Debian:11(1)
PackageVulnerable rangeFixed inDependents
ffmpeg7:4.3.2-0+deb11u2, 7:4.3.2-1, 7:4.3.2-27:4.3.3-0+deb11u1—
Debian:12(1)
PackageVulnerable rangeFixed inDependents
ffmpeg—7:4.4.1-1—
Debian:13(1)
PackageVulnerable rangeFixed inDependents
ffmpeg—7:4.4.1-1—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
ffmpeg—7:4.4.1-1—
Debian:9(1)
PackageVulnerable rangeFixed inDependents
ffmpeg7:3.2.10-1~deb9u1 ... 7:3.2.9-1~deb9u1 (14 versions)7:3.2.16-1+deb9u1—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

All Vendor Advisories

(2)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 7× in last 7d / 31× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 140 total refreshes for this CVE.

  1. 2026-08-25 13:46 UTCEPSS rescore
  2. 2026-08-24 14:13 UTCEPSS rescore
  3. 2026-08-23 00:16 UTCEPSS rescore
  4. 2026-08-21 23:46 UTCEPSS rescore
  5. 2026-08-20 22:52 UTCEPSS rescore
  6. 2026-08-19 20:34 UTCOSV refresh
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  20. 2026-08-06 13:43 UTCEPSS rescore
  21. 2026-08-05 19:14 UTCEPSS rescore
  22. 2026-08-04 16:17 UTCOSV refresh
  23. 2026-08-04 15:06 UTCEPSS rescore
  24. 2026-08-04 10:34 UTCEPSS rescore
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  1. 2026-08-02 02:24 UTCEPSS rescore
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  5. 2026-07-30 01:28 UTCEPSS rescore
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  7. 2026-07-26 14:52 UTCEPSS rescore
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  9. 2026-07-25 14:15 UTCEPSS rescore
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  11. 2026-07-23 14:16 UTCEPSS rescore
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  13. 2026-07-23 02:03 UTCEG score recompute
  14. 2026-07-22 22:49 UTCEG score recompute
  15. 2026-07-22 14:06 UTCEPSS rescore
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  20. 2026-07-19 14:29 UTCEPSS rescore
  21. 2026-07-19 14:29 UTCEPSS rescore
  22. 2026-07-19 02:27 UTCEPSS rescore
  23. 2026-07-18 13:59 UTCOSV refresh
  24. 2026-07-18 10:02 UTCEPSS rescore
  25. 2026-07-18 10:02 UTCEPSS rescore
  26. 2026-07-16 17:00 UTCEPSS rescore
  27. 2026-07-16 17:00 UTCEPSS rescore
  28. 2026-07-15 16:55 UTCEPSS rescore
  29. 2026-07-15 01:58 UTCEPSS rescore
  30. 2026-07-13 22:27 UTCEPSS rescore
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  36. 2026-07-09 19:07 UTCEPSS rescore
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  40. 2026-07-06 02:21 UTCEPSS rescore
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  45. 2026-07-01 15:04 UTCEPSS rescore
  46. 2026-06-30 23:20 UTCEPSS rescore
  47. 2026-06-30 23:20 UTCEPSS rescore
  48. 2026-06-30 18:00 UTCOSV refresh
  49. 2026-06-29 14:04 UTCEPSS rescore
  50. 2026-06-28 14:05 UTCEPSS rescore
  51. 2026-06-28 04:54 UTCEPSS rescore
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  53. 2026-06-27 03:06 UTCEPSS rescore
  54. 2026-06-25 13:48 UTCEPSS rescore
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  67. 2026-06-18 17:51 UTCEPSS rescore
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  74. 2026-06-13 22:58 UTCEPSS rescore
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Frequently asked(5)

What is CVE-2021-38171?
CVE-2021-38171 is a critical vulnerability published on August 21, 2021. adtsdecodeextradata in libavformat/adtsenc.c in FFmpeg 4.4 does not check the initgetbits return value, which is a necessary step because the second argument to initgetbits can be crafted.
When was CVE-2021-38171 disclosed?
CVE-2021-38171 was first published in the National Vulnerability Database on August 21, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-38171 actively exploited?
CVE-2021-38171 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 2% probability of exploitation in the next 30 days, which ranks it in the top 17.2% of all scored CVEs.
What is the CVSS score of CVE-2021-38171?
CVE-2021-38171 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2021-38171?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-38171, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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