major vulnerability· requires attention

FFmpeg is a widely embedded multimedia library; an exploitable heap overflow can enable RCE in many applications and services across organizations.

Applications

CVE-2026-125203

8.5

High

EPSS n/aPatch available

Heap overflow in FFmpeg Cook decoder enabling memory corruption/RCE from crafted RealMedia streams

exploited

No known exploitation not in CISA KEV as of our last sync

fix

Patch available see the advisory in the references

likelihood

No EPSS score yet

Published 9 Nov 2026Analysed here 10 Nov 2026CVSS scored by the publisher (CNA)

common questions

Is CVE-2026-125203 being exploited?

Not confirmed. CVE-2026-125203 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked.

How severe is CVE-2026-125203?

CVE-2026-125203 is rated High with a CVSS score of 8.5. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.

Is there a patch for CVE-2026-125203?

Yes. A fix has been recorded for CVE-2026-125203. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.

What does CVE-2026-125203 affect?

CVE-2026-125203 affects FFmpeg < 8.1.3, FFmpeg 9.x < 9.0.2, Any application using libavcodec Cook multichannel decoder (libavcodec/cook.c). Confirm the exact affected versions against the vendor advisory before deciding you are exposed.

What should I do about CVE-2026-125203?

Upgrade FFmpeg to 8.1.3 or 9.0.2+; block or sanitize untrusted RealMedia files.

Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.

executive summary

technical analysis

affected

FFmpeg < 8.1.3FFmpeg 9.x < 9.0.2Any application using libavcodec Cook multichannel decoder (libavcodec/cook.c)

impact

Heap buffer overflow when decoding crafted RealMedia Cook streams; allows memory corruption, crashes, or remote code execution in apps using vulnerable FFmpeg.

action required

Immediate action required

affected versions

FFmpeg

affected< 8.1.3
affected>= 9.0 and < 9.0.2

As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.

timeline

9 Nov 2026Published
9 Nov 2026CVE record last updated · same day later
10 Nov 2026Analysed by vulneraibility.com · same day later

how to fix

Remediation steps are tailored for users whose stack is affected. Add this technology to your stack to see the fix checklist.

references

NVD CVE.org CVE Details Source

5 references in the CVE record: 1 advisory, 1 patch, 3 links

Advisoryvulncheck.com /advisories/ffmpeg-before-8.1.3-and-9-x-before-9.0.2-heap-buffer-overflow-in-coo
Patchgithub.com /FFmpeg/FFmpeg/commit/3e09f5e24eb277a6d011745ff03e602f61c5c171
Linkcode.ffmpeg.org /FFmpeg/FFmpeg/pulls/24485
Linkgithub.com /FFmpeg/FFmpeg/blob/n9.0.1/libavcodec/cook.c#L1294
Linkgithub.com /FFmpeg/FFmpeg

sources

CVE List (CVE.org): description, affected versions, references; CVE Terms of Use
NVD: CVSS and CPE data
FIRST EPSS: exploit probability and percentile
Summary, impact and triage tags: written by our AI analysis pipeline from the sources above. Check them against the sources.

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