FFmpeg through 9.0.2 Heap Buffer Overflow via DVB Subtitle Encoder

Advisories

FFmpeg through 9.0.2 Heap Buffer Overflow via DVB Subtitle Encoder

Severity: high
Date: 11/9/2026
Affecting: FFmpeg <= 9.0.2
CVE: CVE-2026-125233
CWE: CWE-131 Incorrect Calculation of Buffer Size
CVSS: 8.5
CVSS V4 Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
References: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/24913
Patch Commit
https://github.com/FFmpeg/FFmpeg/blob/n9.0.2/libavcodec/dvbsubenc.c#L363
https://github.com/FFmpeg/FFmpeg
Credit: Secbuddy, Tencent Keen Security Lab (tested by kvartet), Joshua Rogers (AISLE Research), Michael Niedermayer
Description: FFmpeg through 9.0.2 contains a heap buffer overflow vulnerability in dvbsub_encode() in libavcodec/dvbsubenc.c that undercounts each CLUT segment header by two bytes. Attackers can supply a file with many bitmap subtitle rectangles that, when transcoded to the dvbsub encoder, writes past the output buffer and corrupts heap memory.

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