CVE Alert: CVE-2026-121941 – munt

libmt32emu before 2.8.4 contains a heap buffer overflow vulnerability in MidiStreamParserImpl::parseSysex that allows attackers to write past a heap allocation by supplying oversized unterminated SysEx messages. Attackers can feed more than 32768 SysEx data bytes through the mt32emu_parse_stream API via MIDI files, ports, or sequencer clients to corrupt heap memory and crash the application.

**Risk verdict:** Remediate promptly in affected deployments: a proof-of-concept is recorded, but active exploitation and KEV status are not provided, and EPSS is unavailable.

**Why this matters:** Malformed MIDI input could corrupt memory in the process using the library, causing crashes or potentially compromising that process’s confidentiality and integrity. Realistic attacker goals include disrupting audio or game services, or gaining control within an application that processes attacker-supplied MIDI.

**Most likely attack path:** An attacker supplies a crafted MIDI file or stream for a user or service to process; the local attack vector and passive user interaction indicate input handling is the key precondition, with no elevated privileges required. Scope is unchanged, so direct impact is expected within the affected process rather than automatically extending to other systems.

**Who is most exposed:** Workstations and services running MIDI sequencers, synthesiser emulators, games, or other applications that bundle the library and process untrusted MIDI files or live input.

Review crashes and memory-safety alerts in MIDI-handling processes.

Trace oversized or unterminated SysEx messages in MIDI files and stream inputs.

Identify applications loading the affected library and correlate unexpected process restarts.

Mitigation and prioritisation

Upgrade to the fixed release or later; prioritise internet-facing or shared MIDI-processing services.

Until upgraded, block untrusted MIDI files and restrict MIDI stream sources.

Use process sandboxing and least privilege to limit impact.

Test representative MIDI workflows before rollout; no KEV or EPSS data is supplied to support a priority-1 classification.

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