Fluidsynth: From 2.5.0 until 2.5.6, the SF2 parser computes the DMOD modulator count as chunk.size / SF_MOD_SIZE - 1 without rejecting chunks smaller than one… (CVE-2026-61720)
FluidSynth versions from 2.5.0 up to but not including 2.5.6 contain a vulnerability in the SF2 parser where a crafted SoundFont 2 (SF2) file with a zero-sized DMOD chunk causes an unsigned integer underflow. This results in the parser attempting to allocate an extremely large number of SFMod structures, exhausting process memory and causing a denial of service. The issue is fixed in version 2.5.6.
AI Analysis
Technical Summary
In FluidSynth versions 2.5.0 through 2.5.5, the SF2 parser calculates the DMOD modulator count as chunk.size divided by SF_MOD_SIZE minus one, without validating that the chunk size is at least one record. A maliciously crafted SF2 file with a zero-sized DMOD chunk causes the unsigned subtraction to wrap to UINT_MAX, leading the parser to allocate billions of SFMod structures. This memory exhaustion results in denial of service. The vulnerability is resolved in FluidSynth 2.5.6.
Potential Impact
An attacker can cause a denial of service by providing a specially crafted SF2 file that triggers excessive memory allocation in the FluidSynth parser, leading to process memory exhaustion and application crash or hang. There is no impact on confidentiality or integrity reported.
Mitigation Recommendations
This vulnerability is fixed in FluidSynth version 2.5.6. Users should upgrade to version 2.5.6 or later to remediate this issue. No workaround or temporary fix is available.
Fluidsynth: From 2.5.0 until 2.5.6, the SF2 parser computes the DMOD modulator count as chunk.size / SF_MOD_SIZE - 1 without rejecting chunks smaller than one… (CVE-2026-61720)
Description
FluidSynth versions from 2.5.0 up to but not including 2.5.6 contain a vulnerability in the SF2 parser where a crafted SoundFont 2 (SF2) file with a zero-sized DMOD chunk causes an unsigned integer underflow. This results in the parser attempting to allocate an extremely large number of SFMod structures, exhausting process memory and causing a denial of service. The issue is fixed in version 2.5.6.
CVSS v3.1
Score 6.2medium
Affected software
pkg:deb/ubuntu/fluidsynth?arch=source&distro=trustypkg:deb/ubuntu/fluidsynth?arch=source&distro=xenialpkg:deb/ubuntu/fluidsynth?arch=source&distro=bionicpkg:deb/ubuntu/fluidsynth?arch=source&distro=focalpkg:deb/ubuntu/fluidsynth?arch=source&distro=jammypkg:deb/ubuntu/fluidsynth?arch=source&distro=noblepkg:deb/ubuntu/fluidsynth?arch=source&distro=resoluteRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
In FluidSynth versions 2.5.0 through 2.5.5, the SF2 parser calculates the DMOD modulator count as chunk.size divided by SF_MOD_SIZE minus one, without validating that the chunk size is at least one record. A maliciously crafted SF2 file with a zero-sized DMOD chunk causes the unsigned subtraction to wrap to UINT_MAX, leading the parser to allocate billions of SFMod structures. This memory exhaustion results in denial of service. The vulnerability is resolved in FluidSynth 2.5.6.
Potential Impact
An attacker can cause a denial of service by providing a specially crafted SF2 file that triggers excessive memory allocation in the FluidSynth parser, leading to process memory exhaustion and application crash or hang. There is no impact on confidentiality or integrity reported.
Mitigation Recommendations
This vulnerability is fixed in FluidSynth version 2.5.6. Users should upgrade to version 2.5.6 or later to remediate this issue. No workaround or temporary fix is available.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- UBUNTU-CVE-2026-61720
- Osv Schema Version
- 1.7.0
- Ecosystems
- ["Ubuntu:14.04:LTS","Ubuntu:16.04:LTS","Ubuntu:18.04:LTS","Ubuntu:20.04:LTS","Ubuntu:22.04:LTS","Ubuntu:24.04:LTS","Ubuntu:26.04:LTS"]
- Cvss Version
- 3.1
Threat ID: 6ab4be5ef7a7c54106f0aa82
Added to database: 09/24/2026, 06:08:30 UTC
Last enriched: 09/24/2026, 06:49:24 UTC
Last updated: 09/25/2026, 01:47:44 UTC
Views: 4
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