CVE-2026-49417 Overview
CVE-2026-49417 is a use-after-free vulnerability [CWE-416] in the FreeBSD sound subsystem. The audio buffer backing a memory mapping can be freed when the /dev/dsp device is closed while the mapping remains valid. Freed memory may then be reused elsewhere while still accessible through the stale mapping, giving an unprivileged local user a primitive to read and write kernel memory.
The /dev/dsp device nodes are world-accessible by default on FreeBSD systems with an audio device. This exposure turns the flaw into a practical local privilege escalation path on affected FreeBSD 14.3, 14.4, and 15.0 installations.
Critical Impact
An unprivileged local user on a FreeBSD host with an audio device can read and write kernel memory through a stale audio buffer mapping, enabling full system compromise or kernel panic.
Affected Products
- FreeBSD 14.3 (base release through patch level p14)
- FreeBSD 14.4 (base release through patch level p5)
- FreeBSD 15.0 (base release through patch level p9)
Discovery Timeline
- 2026-06-27 - CVE-2026-49417 published to NVD
- 2026-07-01 - Last updated in NVD database
Technical Details for CVE-2026-49417
Vulnerability Analysis
The FreeBSD sound driver exposes audio buffers to userspace through mmap() on /dev/dsp device nodes. When a process maps the audio buffer and the device is subsequently closed, the kernel frees the backing buffer while leaving the userspace virtual mapping intact. The mapping continues to resolve to physical memory that the kernel allocator may reassign to other in-kernel objects.
A local attacker who retains the stale mapping gains a read/write window into arbitrary kernel data structures that later occupy the reused memory. This provides the primitives required to overwrite credential structures, function pointers, or page tables and escalate to root. Because /dev/dsp is world-accessible by default, exploitation requires only an unprivileged shell on a system with a sound device.
Root Cause
The defect is a lifetime-management error between the audio buffer object and the virtual memory object created by mmap(). The close path releases the buffer without invalidating or holding a reference for outstanding mappings, producing the classic use-after-free condition tracked as [CWE-416].
Attack Vector
Exploitation is local and requires an interactive account or code execution as any user. The attacker opens /dev/dsp, calls mmap() on the audio buffer, closes the device to trigger the free, then sprays kernel allocations to place a target object in the freed region. Reads and writes through the retained mapping then manipulate that object. At minimum, an attacker can dereference invalid memory to crash the kernel and cause a denial of service.
// Conceptual exploitation flow - no verified PoC available
// 1. fd = open("/dev/dsp", O_RDWR)
// 2. ptr = mmap(NULL, len, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0)
// 3. close(fd) // audio buffer freed, mapping retained
// 4. spray kernel allocations of size ~len to reuse freed pages
// 5. read/write *ptr to tamper with adjacent kernel objects
Detection Methods for CVE-2026-49417
Indicators of Compromise
- Unexpected processes opening /dev/dsp or /dev/dsp* device nodes on servers without a legitimate audio workload.
- Kernel panics or page fault in kernel mode messages in /var/log/messages originating from the sound module.
- Unprivileged processes performing large numbers of mmap() calls followed by close() on audio devices.
Detection Strategies
- Audit /dev/dsp* access with auditd rules and alert on non-audio service accounts opening these nodes.
- Correlate mmap and close syscall sequences targeting sound devices from shells or scripting interpreters.
- Monitor kernel crash reports and vmcore files for faults in the sound driver call path.
Monitoring Recommendations
- Forward FreeBSD audit and kernel logs to a centralized analytics platform for retention and correlation.
- Baseline expected consumers of /dev/dsp per host and alert on deviations.
- Track privilege changes on FreeBSD hosts following any sound-driver kernel fault to identify post-exploitation escalation.
How to Mitigate CVE-2026-49417
Immediate Actions Required
- Apply the patches referenced in FreeBSD Security Advisory SA-26:27 to all affected FreeBSD 14.3, 14.4, and 15.0 hosts.
- Reboot systems after patching to ensure the updated kernel and sound module are loaded.
- Inventory FreeBSD systems that expose /dev/dsp and prioritize multi-user hosts and shared build servers.
Patch Information
FreeBSD published fixes in Security Advisory SA-26:27. Consult the FreeBSD Security Advisory SA-26:27 for the exact patch levels, freebsd-update instructions, and source revisions that remediate the use-after-free.
Workarounds
- Restrict permissions on /dev/dsp* device nodes so only trusted audio-service accounts can open them, deviating from the world-accessible default.
- Unload the snd_* kernel modules on servers that do not require audio functionality using kldunload.
- Prevent untrusted local users from obtaining interactive shells on hosts where the sound subsystem cannot be disabled or promptly patched.
# Reduce exposure on hosts without a legitimate audio workload
# 1. Restrict device node permissions via devfs rules
echo 'add path "dsp*" mode 0600 group wheel' >> /etc/devfs.rules
service devfs restart
# 2. Unload sound modules if audio is not required
kldstat | grep snd_
kldunload snd_hda
kldunload sound
# 3. Apply vendor patches
freebsd-update fetch
freebsd-update install
shutdown -r now
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
