CVE-2026-121941 in libmt32emu
Summary
by MITRE • 11/04/2026
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.
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Analysis
by VulDB Data Team • 11/04/2026
The vulnerability identified in libmt32em versions prior to 2.8.4 represents a critical security flaw within the MIDI System Exclusive message parsing logic. Specifically, the issue resides in the MidiStreamParserImpl::parseSysex function, which is responsible for processing SysEx data streams sent by external applications or files. The core technical defect is a heap buffer overflow that occurs when the parser fails to correctly validate the length of incoming SysEx messages against the allocated memory boundaries. This flaw allows an attacker who can supply oversized, unterminated System Exclusive messages to write data beyond the bounds of the intended heap allocation. By exploiting this condition through the mt32emu_parse_stream API, malicious actors can achieve arbitrary code execution or cause a denial of service by corrupting adjacent heap metadata and application memory structures.
From a technical perspective, the vulnerability stems from insufficient boundary checks during the parsing phase of MIDI data streams. When an attacker provides more than 32768 bytes of SysEx data via MIDI files, network ports, or sequencer clients, the parser does not adequately truncate or reject the input before writing it to memory. This lack of validation leads to a classic heap overflow scenario where contiguous memory regions are overwritten with maliciously crafted data. The operational impact is severe, as heap corruption typically results in immediate application crashes due to segmentation faults triggered by invalid memory access attempts during subsequent operations such as garbage collection or pointer dereferencing. In more sophisticated attack scenarios, this memory corruption can be leveraged to hijack control flow, potentially leading to remote code execution if the vulnerable library is integrated into a service that processes untrusted MIDI input from network sources.
This vulnerability aligns with Common Weakness Enumeration (CWE) category CWE-120, which describes buffer copies without checking size constraints, and more specifically reflects aspects of CWE-787, out-of-bounds write vulnerabilities in heap memory. In the context of the MITRE ATT&CK framework, this flaw facilitates techniques associated with initial exploitation via input validation failures, often categorized under Tactic TA0001 Initial Access or TA0004 Impact depending on whether the goal is intrusion or disruption. The ability to crash applications through denial-of-service attacks places it within the scope of availability-focused threats, while potential code execution vectors relate to privilege escalation and arbitrary command execution capabilities.
Mitigation strategies primarily involve upgrading libmt32em to version 2.8.4 or later, where this parsing logic has been corrected to enforce strict length limits on SysEx messages. Developers integrating this library should also implement input sanitization layers that validate MIDI data structures before passing them to the parser API. Additionally, employing memory-safe programming practices and utilizing static analysis tools can help detect similar buffer overflow conditions in related codebases. For systems where immediate patching is not feasible, deploying network-level filtering rules to restrict the size of incoming MIDI streams or disabling direct access to sequencer clients from untrusted networks can serve as temporary compensating controls to reduce the attack surface associated with this heap corruption vulnerability.