Executive brief
FreeRDP is a widely-used open-source client for connecting to remote desktops via the Remote Desktop Protocol. A malicious RDP server can trigger a heap buffer overflow in the audio codec when negotiating Opus audio format, allowing it to corrupt client memory, crash the application, or potentially execute arbitrary code on the victim's machine.
Technical details
The vulnerability is a heap buffer overflow in the freerdp_dsp_decode_opus function (libfreerdp/codec/dsp.c). The bug occurs because the code performs capacity checks on context->common.buffer, but the underlying opus_decode library writes decoded PCM audio into the caller-supplied output stream without respecting that buffer's bounds. When a client has Opus support enabled (WITH_OPUS) but FFmpeg DSP disabled (WITH_DSP_FFMPEG disabled), a malicious RDP server can negotiate WAVE_FORMAT_OPUS and send a large decoded audio frame (up to 5760 samples at 48 kHz) that exceeds the 4096-byte StreamPool allocation in rdpsnd_main.c, causing heap corruption. The attack requires network-level access to the RDP connection and no authentication bypass; the server-side negotiation is sufficient. This was fixed in version 3.28.0 by correcting buffer validation logic.
Affected products
- FreeRDP FreeRDP prior to 3.28.0
Timeline
- 2026-08-19: disclosed
- 2026-07-02: patched: Fix merged into master branch; released in version 3.28.0