Executive brief
FreeBSD's sound driver handles synchronization of multiple audio devices through a kernel ioctl interface. A use-after-free vulnerability in this interface allows unprivileged local users on systems with multiple audio devices to escalate privileges by exploiting a race condition in lock management. Systems with zero or one sound device are unaffected.
Technical details
The SNDCTL_DSP_SYNCSTART ioctl implementation attempts to acquire locks on all channels in a sync group. When locking a channel would block, it releases the sync group list lock and sleeps. Upon reawakening, the sync group structure may have been freed, but the implementation does not validate this, resulting in a use-after-free vulnerability. The vulnerability requires local access and multiple audio devices present on the system. An unprivileged local user can exploit this race condition to achieve privilege escalation. Patches were issued on 2026-08-25 for all supported FreeBSD branches.
Affected products
- FreeBSD FreeBSD 15.0, 15.1, 14.4 and earlier supported versions
Timeline
- 2026-08-25: disclosed: FreeBSD Security Advisory SA-26:58 published
- 2026-08-25: patched: Patches released for stable/15, releng/15.1, releng/15.0, stable/14, and releng/14.4