CVE-2026-61714

FluidSynth is a software synthesizer based on the SoundFont 2 specifications. From 2.2.4 until 2.5.6, configuring synth.midi-channels above 16 allows the MIDI player to index _fluid_player_t::channel_isplaying outside its fixed-size heap allocation while tracking active channels. The resulting out-of-bounds reads and writes invoke undefined behavior and may compromise confidentiality, integrity, or availability. No crafted MIDI file is required because the unsafe condition is created by the channel-count configuration itself. Keeping synth.midi-channels at its default value of 16 avoids the vulnerable path. This issue is fixed in version 2.5.6.

• https://github.com/FluidSynth/fluidsynth/commit/772702e00cc6acc7c607efb40283e2269211effc
• https://github.com/FluidSynth/fluidsynth/releases/tag/v2.5.6
• https://github.com/FluidSynth/fluidsynth/security/advisories/GHSA-976m-35rw-h3m6