# CVE-2026-58264: FluidSynth: Heap-based buffer overrun

> An out-of-bounds heap write in FluidSynth's command handler allows remote attackers to cause denial of service or execute code when the TCP server is enabled.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Sep 2026
- **Updated:** 21 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-58264, ECHO-c5c2-10b5-9d2d, GHSA-mqmq-w63q-cj94, OESA-2026-2959, OESA-2026-2960, OESA-2026-2961, OESA-2026-3081, UBUNTU-CVE-2026-58264, openSUSE-SU-2026:11211-1

## What is CVE-2026-58264?

CVE-2026-58264 is a critical memory corruption vulnerability in fluidsynth, published on 18 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

FluidSynth is a software synthesizer based on the SoundFont 2 specifications. From 1.1.2 until 2.5.6, the FluidSynth command handler accepts a pitch_bend_range command whose channel argument is not bounds checked before the supplied value is written through the selected synth channel. An out-of-range channel can therefore cause an out-of-bounds heap write, leading to denial of service or possible code execution. The issue is remotely reachable when the TCP server is enabled through new_fluid_server() or fluidsynth -s, and it is locally reachable through malicious commands delivered to the FluidSynth shell on standard input. Applications that do not use the shell, command handler, or TCP server are not affected. This issue is fixed in version 2.5.6.

Weakness: CWE-122 (Heap-based Buffer Overflow)

## Which versions are affected by CVE-2026-58264?


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `fluidsynth` | openSUSE:Tumbleweed | All versions | 2.5.6-1.1 |

## How do I fix CVE-2026-58264?

Upgrade to a fixed version.

## Is CVE-2026-58264 being exploited?

There is no known exploitation of CVE-2026-58264 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-58264 and fix it if it is affected.

What it is: CVE-2026-58264 is a critical memory corruption vulnerability in fluidsynth, published on 18 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-58264 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-2026-58264/ (Markdown: https://insights.sbomify.com/CVE-2026-58264/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-58264
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-58264
- OSV: https://osv.dev/vulnerability/CVE-2026-58264

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-58264/
Summaries are generated and may contain mistakes; the official description above is the record.