FluidSynth: SF2 DMOD Chunk Unsigned Underflow

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Summary

CVECVE-2026-61720
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-18 20:17:18 UTC
Updated2026-09-24 21:25:27 UTC
DescriptionFluidSynth is a software synthesizer based on the SoundFont 2 specifications. 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 record. A crafted SF2 file containing a zero-sized DMOD chunk makes the unsigned subtraction wrap to UINT_MAX, and the parser then attempts billions of SFMod allocations. This exhausts process memory and causes denial of service. No workaround is available. This issue is fixed in version 2.5.6.

Risk And Classification

Primary CVSS: v3.1 6.2 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS: 0.001840000 probability, percentile 0.070660000 (date 2026-09-25)

Problem Types: CWE-191 | CWE-191 CWE-191: Integer Underflow (Wrap or Wraparound)

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary6.2MEDIUMCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED6.2MEDIUMCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA FluidSynth Fluidsynth affected >= 2.5.0, < 2.5.6 Not specified

References

ReferenceSourceLinkTags
github.com/FluidSynth/fluidsynth/releases/tag/v2.5.6 [email protected] github.com
github.com/FluidSynth/fluidsynth/commit/096e1ff0d09ddcac83d94923440706f7... [email protected] github.com
github.com/FluidSynth/fluidsynth/security/advisories/GHSA-rmc4-c8hw-455w [email protected] github.com
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