# CVE-2026-61720: FluidSynth: SF2 DMOD Chunk Unsigned Underflow

> A crafted SoundFont file triggers an unsigned integer underflow in FluidSynth, causing excessive memory allocation and denial of service.

- **Severity:** Medium 6.2 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Sep 2026
- **Updated:** 21 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-61720, GHSA-rmc4-c8hw-455w, UBUNTU-CVE-2026-61720

## What is CVE-2026-61720?

CVE-2026-61720 is a medium-severity vulnerability in fluidsynth, published on 18 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

FluidSynth 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.

Weakness: CWE-191 (Integer Underflow (Wrap or Wraparound))

## Which versions are affected by CVE-2026-61720?


## How do I fix CVE-2026-61720?

Upgrade to a fixed version.

## Is CVE-2026-61720 being exploited?

There is no known exploitation of CVE-2026-61720 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-61720 and fix it if it is affected.

What it is: CVE-2026-61720 is a medium-severity vulnerability in fluidsynth, published on 18 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-61720 in the wild and no public exploit code.

Affected product: fluidsynth. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-61720/ (Markdown: https://insights.sbomify.com/CVE-2026-61720/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-61720
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-61720
- OSV: https://osv.dev/vulnerability/CVE-2026-61720

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-61720/
Summaries are generated and may contain mistakes; the official description above is the record.