# CVE-2026-121941: libmt32emu before 2.8.4 Heap Buffer Overflow via MidiStreamParserImpl::parseSysex

Status: published. Published: 2026-11-04. Updated: 2026-11-04.

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.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/munt/munt/commit/1749f7fed5cdb3a9015acce076a1512b1615dc3b

## Affected products and versions

- munt / libmt32emu (munt/munt): ≥ 0; < 2.8.4 (affected, semver). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 4.0: 8.5 (high); CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N; source: CNA: VulnCheck

- CVSS 3.1: 7.8 (high); CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H; source: CNA: VulnCheck

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-122

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/munt/munt/issues/149 (CNA: VulnCheck; issue-tracking)

- https://hackmd.io/@haindpwn/munt-midistreamparser-oversized-sysex-heap-overflow (CNA: VulnCheck; third-party-advisory)

- https://github.com/munt/munt/commit/1749f7fed5cdb3a9015acce076a1512b1615dc3b (CNA: VulnCheck; patch)

- https://github.com/munt/munt/blob/libmt32emu_2_8_3/mt32emu/src/MidiStreamParser.cpp#L223-L257 (CNA: VulnCheck; technical-description)

- https://www.vulncheck.com/advisories/libmt32emu-before-2.8.4-heap-buffer-overflow-via-midistreamparserimpl-parsesysex (CNA: VulnCheck; third-party-advisory)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-121941; retrieved 2026-11-04; source updated 2026-11-04

Revision: 3125fd7ddebcfe48ed58bd4418739ff96e16f7e4288ae7c261546280b221370e

Canonical: https://y2.dev/cve/CVE-2026-121941

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