CVE-2026-43257 Overview
CVE-2026-43257 is a resource management flaw in the Linux kernel's cx88 media driver. The vulnerability resides in the snd_cx88_hw_params() function within the ALSA sound subsystem of the cx88 driver. When the function encounters an error path after calling cx88_alsa_dma_map(), it fails to invoke the corresponding cx88_alsa_dma_unmap() to release the previously acquired DMA resources. This omission produces a kernel-level resource leak that accumulates across repeated failure events. The Linux kernel maintainers resolved the issue by adding the missing unmap call in the error path.
Critical Impact
Repeated invocations along the failure path leak DMA mapping resources in kernel space, which can degrade system stability over time on hosts using cx88-based capture hardware.
Affected Products
- Linux kernel media: cx88 driver (ALSA component)
- Multiple stable kernel branches receiving backports across the referenced commits
- Systems with Conexant CX2388x-based TV/capture cards loading the cx88-alsa module
Discovery Timeline
- 2026-05-06 - CVE-2026-43257 published to the National Vulnerability Database
- 2026-05-06 - Last updated in NVD database
Technical Details for CVE-2026-43257
Vulnerability Analysis
The defect lies in snd_cx88_hw_params(), the hardware parameter setup routine for the cx88 ALSA driver. The function allocates a DMA mapping by invoking cx88_alsa_dma_map() to prepare buffers for audio capture. If a subsequent step within the function fails, control returns to the caller without releasing the DMA mapping. The mapping remains pinned in kernel memory with no remaining reference for cleanup.
This represents a classic memory leak pattern in kernel error-handling code [CWE-401]. Each failure path execution increments leaked resource accounting. On long-running systems that exercise the cx88 audio path repeatedly under failure conditions, the leak can exhaust DMA-capable memory regions and degrade kernel stability.
Root Cause
The root cause is asymmetric resource handling between the success and error paths of snd_cx88_hw_params(). The function acquires a DMA mapping but lacks a goto-style cleanup label or explicit cx88_alsa_dma_unmap() call before returning the error. The fix introduces the missing unmap call, restoring symmetry between acquisition and release.
Attack Vector
The vulnerability requires the cx88-alsa driver to be loaded and exercised. Triggering the leak depends on inducing failures inside snd_cx88_hw_params(), which is reachable through standard ALSA ioctl() interfaces from userspace processes that have access to the corresponding /dev/snd/ PCM device. Repeated triggering accumulates leaked DMA resources over the system's uptime.
For the specific code change, see the upstream patches: Kernel Patch Commit 10ab64f, Kernel Patch Commit 1ce8c2a, Kernel Patch Commit 24f3dab, Kernel Patch Commit 3baefeeb, Kernel Patch Commit dbc527d, Kernel Patch Commit dc911fcc, Kernel Patch Commit e3fb15aa, and Kernel Patch Commit f0d7f735.
Detection Methods for CVE-2026-43257
Indicators of Compromise
- Steadily growing kernel SUnreclaim or Slab values reported in /proc/meminfo on hosts with cx88 hardware in use.
- DMA allocation failures or dma_alloc_coherent warnings appearing in dmesg over extended uptime.
- Audio capture initialization failures from the cx88-alsa module recurring without driver reload.
Detection Strategies
- Audit running kernel versions against the patched stable releases referenced by the upstream commits.
- Inventory hosts loading the cx88_alsa kernel module via lsmod and confirm patch status.
- Track kernel memory growth trends over time and correlate against ALSA error events for cx88 devices.
Monitoring Recommendations
- Monitor dmesg for cx88 driver error returns from snd_cx88_hw_params().
- Alert on sustained kernel slab growth that does not correlate with workload increases.
- Forward kernel logs to centralized log collection for correlation across the affected fleet.
How to Mitigate CVE-2026-43257
Immediate Actions Required
- Apply the upstream stable kernel update containing the cx88_alsa_dma_unmap() fix from the referenced commits.
- Identify systems running cx88-based capture hardware and prioritize them for kernel update scheduling.
- Restrict access to /dev/snd/ PCM nodes to trusted users on multi-user hosts running unpatched kernels.
Patch Information
The fix adds the missing cx88_alsa_dma_unmap() call in the error path of snd_cx88_hw_params(). The patch has been merged across multiple Linux stable trees through commits 10ab64f8, 1ce8c2a8, 24f3dabe, 3baefeeb, dbc527d9, dc911fcc, e3fb15aa, and f0d7f735. Distribution kernels should pick up the change in their next stable rebase.
Workarounds
- Unload the cx88_alsa module with modprobe -r cx88_alsa on systems that do not require cx88 audio capture.
- Blacklist the cx88_alsa module on hosts where the hardware is not used by adding it to /etc/modprobe.d/blacklist.conf.
- Reboot affected hosts on a defined cadence to reclaim leaked DMA resources until the patched kernel is deployed.
# Configuration example
# Blacklist the cx88_alsa module until a patched kernel is installed
echo "blacklist cx88_alsa" | sudo tee /etc/modprobe.d/cx88-cve-2026-43257.conf
sudo modprobe -r cx88_alsa
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
