Executive brief
FluidSynth is a software synthesizer that reads and plays sound files in DLS format. A flaw in the DLS parser allows an attacker to create a malicious sound file that causes the application to allocate massive amounts of memory and read far beyond file boundaries when the file is opened or parsed, leading to denial of service or application crash.
Technical details
The native DLS parser fails to check for integer overflow when computing the chunk size using the expression cues * 4 + cbsize, where cues is read from an untrusted DLS file. An attacker can supply a large cues value that wraps the 32-bit arithmetic, bypassing the bounds check and causing subsequent resize operations to request gigabytes of memory and read invalid memory beyond chunk boundaries. The vulnerability exists only when the enable-native-dls option is enabled.
Affected products
- FluidSynth FluidSynth 2.5.0 to 2.5.5
Timeline
- 2026-09-18: disclosed
- 2026-07-04: patched: Version 2.5.6 released with fix