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Use after free in fluidsynth

High
derselbst published GHSA-ffw2-xvvp-39ch Dec 23, 2025

Package

fluidsynth

Affected versions

>= 2.5.0, < 2.5.2

Patched versions

2.5.2

Description

Impact

A race condition during unloading of a DLS file can trigger a heap-based use-after-free. A concurrently running thread may be pending to unload a DLS file, leading to use of freed memory, if

  • the synthesizer is being concurrently destroyed, or
  • samples of the (unloaded) DLS file are concurrently used to synthesize audio.

Realistically, both scenarios will result in a denial of service. In worst cases, it may result in arbitrary code execution in the context of an application using FluidSynth.

Patches

Update to 2.5.2 or later.

Workarounds

The problem will not occur, when explicitly unloading a DLS file (before synth destruction), provided that at the time of unloading, no samples of the respective file are used by active voices.
The problem will not occur in versions of FluidSynth that have been compiled without native DLS support.

References

#1728, #1717

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Local
Attack complexity
High
Privileges required
None
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

CVE ID

CVE-2025-68617

Weaknesses

Use After Free

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer. Learn more on MITRE.

Credits