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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
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
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.
Sources
Also known as DEBIAN-CVE-2026-61720, GHSA-rmc4-c8hw-455w, UBUNTU-CVE-2026-61720.