CVE-2026-125103: FFmpeg heap disclosure in MLZ decoder

Summary

FFmpeg through 9.0.2 contains an information disclosure vulnerability in ff_mlz_decompression() in libavcodec/mlz.c, which accepts string codes beyond the dictionary's next free code. Attackers can supply a crafted MPEG-4 ALS file with malformed initial or out-of-range codes to copy uninitialized heap bytes into decoded audio output.

cve.now Index

5Pcve.now Index 5 of 100 · methodology v3 · provisional

Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
Exposure?/25Unknown. No advisory context yet
Reach?/20Unknown. No tracked technology or package matched
Severity4.8/10CVSS 4.8
No patch0/5No signal

What would change the score

Would score about 60 if added to CISA KEV
Would score about 55 if CISA's SSVC rates exploitation active
Would score about 27 if advisories confirm default setups are exposed

How the score works · Rankings

What to do

Apply the patch listed under Evidence.

Timeline

Nov 9, 2026, 7:10 PM UTCCVE published
Nov 9, 2026, 7:15 PM UTCFirst seen by cve.now

Affected versions

FFmpeg FFmpeg
through 9.0.2

Evidence 5

Corrections

None so far.

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Questions about CVE-2026-125103

Is CVE-2026-125103 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data

Which versions are affected by CVE-2026-125103?

FFmpeg: through 9.0.2.Source: cve.now feed data

FFmpeg through 9.0.2 Uninitialized Heap Disclosure via MLZ Decompressor in ALS Decoder