Heap Buffer Overflow in FFmpeg's DVB Subtitle Encoder

CVE-2026-125233

What is CVE-2026-125233?

FFmpeg, up to version 9.0.2, is susceptible to a heap buffer overflow vulnerability specifically within the dvbsub_encode() function in libavcodec/dvbsubenc.c. This flaw arises due to an incorrect calculation that undercounts each CLUT (Color Lookup Table) segment header by two bytes. Attackers can exploit this vulnerability by supplying crafted files containing numerous bitmap subtitle rectangles. During transcoding to the dvbsub encoder, the encoder may write beyond the output buffer, potentially leading to heap memory corruption and enabling further exploitation.

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