FluidSynth through 2.6.1 Out-of-Bounds Write via SoundFont Modulator Destination

Advisories

FluidSynth through 2.6.1 Out-of-Bounds Write via SoundFont Modulator Destination

Severity: medium
Date: 10/15/2026
Affecting: fluidsynth <= 2.6.1
CVE: CVE-2026-111123
CWE: CWE-787 Out-of-bounds Write
CVSS: 6.9
CVSS V4 Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N
References: https://hackmd.io/@haind-pwn/fluidsynth-sf2-modulator-dest-generator-oob-write
https://github.com/FluidSynth/fluidsynth/blob/71e85b2ca6bf48641ba7e2261d8f2640ae473773/src/synth/fluid_voice.c#L615-L623
https://github.com/FluidSynth/fluidsynth/blob/71e85b2ca6bf48641ba7e2261d8f2640ae473773/src/synth/fluid_voice.c#L1184-L1229
https://github.com/FluidSynth/fluidsynth/blob/71e85b2ca6bf48641ba7e2261d8f2640ae473773/src/sfloader/fluid_defsfont.c#L1609-L1611
https://github.com/FluidSynth/fluidsynth
Credit: HaiND from the Post and Telecommunication Institute of Technology
Description: FluidSynth through 2.6.1 contains an out-of-bounds write vulnerability that allows attackers to corrupt heap and stack memory by supplying unvalidated SoundFont modulator destination values. Attackers can craft an SF2 file with PMOD/IMOD destinations of 63 to 255 that, when loaded and played, write past the voice generator array and updated_gen_bit, causing memory corruption and crashes.

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