CVE-2026-45258: FreeBSD Privilege Escalation Vulnerability

CVE-2026-45258 Overview

CVE-2026-45258 is an integer overflow vulnerability in the FreeBSD kernel's sound subsystem, specifically within the dsp_mmap_single() function. The flaw exists in the validation logic that checks memory-mapping requests against the audio buffer size. An attacker can supply a crafted offset and length whose sum overflows a 64-bit integer, bypassing the size check. The offset is then truncated to 32 bits when converted to a buffer address, producing a mapping that extends past the audio buffer into unrelated kernel memory. Because /dev/dsp device nodes are world-accessible by default, any unprivileged local user on a system with an audio device can exploit this to read and write kernel memory.

Critical Impact
Unprivileged local users can read and write kernel memory through /dev/dsp, enabling full privilege escalation or kernel crashes leading to Denial of Service.

Affected Products

FreeBSD 14.3 (including patches p1 through p14)
FreeBSD 14.4 (including patches p1 through p5)
FreeBSD 15.0 (including patches p1 through p9)

Discovery Timeline

2026-06-27 - CVE-2026-45258 published to NVD
2026-07-01 - Last updated in NVD database

Technical Details for CVE-2026-45258

Vulnerability Analysis

The vulnerability resides in the dsp_mmap_single() function of the FreeBSD sound driver. This function services mmap(2) system calls against /dev/dsp device nodes to map audio buffers into user address space. Before establishing the mapping, the function validates the request by summing the user-supplied offset and length and comparing the total against the audio buffer size. This addition is performed without overflow protection.

An attacker who supplies large values causes the sum to wrap around zero, allowing the check to pass with values that individually exceed the buffer boundary. The kernel then narrows the 64-bit offset to a 32-bit buffer address, producing a mapping whose backing memory lies outside the audio buffer. The resulting mapping grants direct read and write access to adjacent kernel memory regions. This behavior maps to [CWE-125] Out-of-Bounds Read, though the write primitive also enables out-of-bounds write.

Root Cause

The root cause is missing overflow validation in arithmetic used for boundary checking. The check offset + length <= buffer_size fails when the addition wraps in unsigned arithmetic. A secondary defect is the narrowing conversion from 64-bit to 32-bit that discards high-order bits without validation, translating malicious offsets into valid-looking buffer indices.

Attack Vector

Exploitation requires local access to a FreeBSD host with an active audio device. Because /dev/dsp is world-readable and world-writable by default, any local account, including low-privilege service accounts, can open the device and issue mmap(2) with crafted offset and length arguments. The resulting mapping exposes arbitrary kernel memory to userland, providing a primitive for privilege escalation to root or for corrupting kernel structures to trigger a panic.

No verified public exploit code is available at the time of publication. Refer to the FreeBSD Security Advisory SA-26:27 for authoritative technical details.

Detection Methods for CVE-2026-45258

Indicators of Compromise

Unexpected mmap(2) calls against /dev/dsp from processes that do not normally use audio, such as web servers, cron jobs, or shell sessions on production hosts.
Kernel panics or page faults referencing addresses outside the sound driver's expected memory range.
Unprivileged processes suddenly gaining root privileges without a corresponding setuid binary execution in audit logs.

Detection Strategies

Audit mmap system calls targeting /dev/dsp using dtrace or FreeBSD audit framework (auditd) and flag mappings with offsets or lengths approaching SIZE_MAX.
Monitor /var/log/messages and kernel core dumps for panics originating in the sound subsystem, particularly in dsp_mmap_single or adjacent functions.
Correlate process lineage: identify non-audio applications opening /dev/dsp followed by privilege changes.

Monitoring Recommendations

Enable FreeBSD audit trails for AUE_MMAP events and forward them to a centralized log platform for retention and correlation.
Track user-to-root transitions and unexpected UID changes on hosts running vulnerable FreeBSD versions.
Baseline which accounts and services legitimately access /dev/dsp so anomalous access can be alerted on promptly.

How to Mitigate CVE-2026-45258

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.
Inventory FreeBSD systems with the snd_* kernel modules loaded and prioritize multi-user or shell-access hosts.
Restrict local shell access on production systems until patches are deployed, as exploitation requires only unprivileged local access.

Patch Information

FreeBSD has published fixes in Security Advisory SA-26:27. Administrators should apply the vendor-supplied patch using freebsd-update fetch install or rebuild the kernel from patched source. Reboot is required after patching because the fix updates the kernel sound driver. Consult the FreeBSD Security Advisory SA-26:27 for exact patch hashes and version identifiers.

Workarounds

Unload the sound driver on systems that do not require audio: kldunload snd_driver and prevent it from loading at boot by removing entries from /boot/loader.conf.
Tighten permissions on /dev/dsp* device nodes using devfs.rules so only members of a trusted group can open them.
On hosts where audio is not required, remove the snd_* modules from the kernel configuration entirely.

bash

# /etc/devfs.rules - restrict /dev/dsp access to the 'audio' group
[localrules=10]
add path 'dsp*' mode 0660 group audio
add path 'audio*' mode 0660 group audio

# Enable the ruleset in /etc/rc.conf
# devfs_system_ruleset="localrules"

# Apply immediately
service devfs restart