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CVE Record

CVE-2021-38171: adts_decode_extradata in libavformat/adtsenc.c in FFmpeg 4.4 does not check the init_get_bits return value,...

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.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

This is an FFmpeg media-parsing flaw in ADTS/AAC extradata handling. FFmpeg 4.4 failed to check whether a bit-reader initialization succeeded. Organizations using FFmpeg to process user-supplied media should treat this as a media-ingestion risk, but public severity and exploitation evidence in the supplied sources are limited.

Executive priority

Treat as a targeted patch-management item for media-processing environments, not a confirmed emergency. Prioritize externally exposed upload, transcoding, and scanning services using FFmpeg.

Technical view

CVE-2021-38171 affects adts_decode_extradata in libavformat/adtsenc.c in FFmpeg 4.4. The function did not check init_get_bits return value even though the bit-length argument could be crafted. The source bundle references an upstream FFmpeg commit and Debian and Gentoo FFmpeg security updates.

Likely exposure

Exposure is most likely where FFmpeg 4.4 or vulnerable downstream packages process untrusted media files, uploads, streams, or attachments. The supplied affected-product metadata is incomplete beyond FFmpeg 4.4.

Exploitation context

The supplied sources do not show CISA KEV listing or active exploitation. The risk depends on whether attackers can cause vulnerable FFmpeg processing of crafted media, but no exploit chain or real-world abuse evidence is provided.

Researcher notes

Evidence is sparse: no CVSS, CWE, CPE, or KEV signal is included. The central technical issue is unchecked init_get_bits failure in ADTS extradata decoding, with remediation indicated by the referenced FFmpeg commit and distribution advisories.

Mitigation direction

  • Inventory FFmpeg versions in applications, containers, hosts, and embedded media workflows.
  • Apply the relevant upstream, Debian, Gentoo, or vendor FFmpeg security update.
  • Prioritize systems that process untrusted user-uploaded or internet-sourced media.
  • If no packaged fix is available, check current FFmpeg vendor guidance.

Validation and detection

  • Confirm whether FFmpeg 4.4 or affected distribution packages are present.
  • Check whether media workflows invoke FFmpeg on untrusted files or streams.
  • Verify the upstream fix or distribution security update is installed.
  • Review logs for crashes or failures during ADTS/AAC media processing.
Prepared
Confidence
medium
Sources
8

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2021-38171 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
7Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.