CVE-2025-38481

What it actually does

The COMEDI_INSNLIST ioctl accepts an arbitrary n_insns value from user space and attempts a kernel allocation of that size; an excessively large value triggers a WARNING plus stack dump instead of graceful failure.

Why it matters to the business

Unprivileged local users can trigger kernel warnings and stack traces on systems exposing the comedi interface, causing noise in logs, potential automated monitoring alerts, and in extreme cases contributing to system instability.

How an attack unfolds

An attacker with access to a device node handled by the comedi subsystem crafts a COMEDI_INSNLIST ioctl request containing an n_insns value larger than MAX_INSNS, causing the kernel allocation path to emit a warning and stack dump; listed threat actors have been observed chaining similar kernel input-validation issues for privilege escalation on Linux.

How to fix it

Upgrade the Linux kernel to a version containing commit 9772025d24e939fd84b85748ce35c26874c05775 or later that enforces the MAX_INSNS limit and returns -EINVAL for unreasonable values.

How to confirm the fix worked

Confirm the kernel source contains the MAX_INSNS check before the allocation in comedi_ioctl.c; attempt the ioctl with n_insns=65537 and verify it now returns -EINVAL without a kernel warning.

Typical attack path

1. Obtain access to a comedi character device
2. Prepare a struct comedi_insnlist with an oversized n_insns field
3. Invoke the COMEDI_INSNLIST ioctl
4. Observe kernel WARNING and stack trace in dmesg or logs

How to detect it

Search kernel logs and dmesg for comedi allocation warnings containing large n_insns values; correlate with process execution of binaries that open comedi devices.

What your security team should do

• Apply the referenced kernel patch or distribution update immediately on any system exposing comedi devices
• Restrict access to comedi device nodes via udev rules or DAC/MAC policies
• Monitor dmesg and kernel logs for comedi-related WARNING entries