CVE-2026-58264 in FluidSynth
Summary
by MITRE • 09/18/2026
FluidSynth is a software synthesizer based on the SoundFont 2 specifications. From 1.1.2 until 2.5.6, the FluidSynth command handler accepts a pitch_bend_range command whose channel argument is not bounds checked before the supplied value is written through the selected synth channel. An out-of-range channel can therefore cause an out-of-bounds heap write, leading to denial of service or possible code execution. The issue is remotely reachable when the TCP server is enabled through new_fluid_server() or fluidsynth -s, and it is locally reachable through malicious commands delivered to the FluidSynth shell on standard input. Applications that do not use the shell, command handler, or TCP server are not affected. This issue is fixed in version 2.5.6.
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Analysis
by VulDB Data Team • 09/18/2026
FluidSynth serves as a widely utilized software synthesizer adhering to SoundFont specifications, enabling high-quality audio synthesis across various applications and embedded systems. A critical security vulnerability was identified within the command handling mechanism of FluidSynth versions ranging from 1.1.2 through 2.5.6. This flaw specifically affects the pitch_bend_range command handler, which is responsible for adjusting the pitch modulation range on specific MIDI channels. The core technical deficiency lies in the absence of bounds checking for the channel argument provided by the user or remote client before this value is utilized to index into internal data structures associated with synth channels.
When a malicious actor supplies a channel identifier that falls outside the valid operational range, the application proceeds to write data through an invalid pointer derived from this unchecked index. This results in an out-of-bounds heap write operation. Heap corruption of this nature destabilizes the memory management subsystem and can lead to arbitrary code execution if the attacker carefully crafts the payload to overwrite critical function pointers or control flow metadata within adjacent heap chunks. In less exploitable scenarios, the immediate consequence is a segmentation fault or application crash, resulting in a denial of service condition that disrupts audio processing services dependent on FluidSynth.
The attack surface for this vulnerability varies based on how FluidSynth is deployed and configured. The issue is remotely reachable when the TCP server functionality is explicitly enabled via the new_fluid_server API call or by launching the fluidsynth binary with the -s flag, which starts a command-line interface over network connections. In these configurations, an unauthenticated remote attacker can send crafted commands to trigger the heap overflow. Additionally, the vulnerability is locally reachable through malicious inputs delivered directly to the FluidSynth shell on standard input, affecting users who interact with the interactive command line interface without proper validation of their inputs.
Applications that do not utilize the interactive shell, the TCP server component, or direct command handling interfaces are generally unaffected by this specific flaw, as they typically bypass the vulnerable code path entirely. This distinction highlights the importance of minimizing attack surfaces in software deployment; disabling unnecessary services reduces exposure to remote exploitation vectors. The vulnerability is classified under CWE-787: Out-of-bounds Write, which describes writing data outside the boundaries of allocated memory, and aligns with ATT&CK techniques related to execution via command injection or local privilege escalation depending on the context of access.
The issue has been resolved in version 2.5.6 through rigorous input validation that ensures channel identifiers are strictly checked against valid bounds before being used for array indexing or pointer arithmetic. Developers integrating FluidSynth into their products should immediately upgrade to this patched version to mitigate the risk of heap corruption and potential remote code execution. For systems where upgrading is not immediately feasible, disabling the TCP server and restricting access to the interactive shell can serve as a temporary mitigation strategy to prevent exploitation by untrusted parties.