CVE-2025-38478

What it actually does

Kernel buffers allocated for Comedi write instructions in do_insn_ioctl and do_insnlist_ioctl contain uninitialized data beyond the first insn->n elements (up to MIN_SAMPLES), allowing subdevice handlers to read kernel stack or heap memory.

Why it matters to the business

Attackers with access to Comedi devices on affected Linux systems could obtain fragments of sensitive kernel memory contents, increasing risk of credential or secret leakage in environments running the vulnerable kernel.

How an attack unfolds

An attacker with local access issues Comedi write instructions via ioctl that trigger subdevice handlers known to read beyond the copied user data; the handler then returns or leaks the uninitialized kernel memory back to user space. Listed threat actors have been observed chaining similar kernel memory disclosure primitives for privilege escalation.

How to fix it

Update the Linux kernel to a version containing commit 6f38c6380c3b38a05032b8881e41137385a6ce02 or later; rebuild and reboot. For Debian 14 packages named stardict, ensure version 3.0.7+git20220909+dfsg-7 or newer is installed. Apply vendor kernel updates promptly given the 456 days since publication and rising EPSS trend.

How to confirm the fix worked

Confirm the running kernel git commit or package version contains 6f38c6380c3b38a05032b8881e41137385a6ce02; recompile a test module that exercises write instructions and verify no uninitialized bytes are returned in the data buffer.

Typical attack path

1. Obtain local user access on a system exposing /dev/comedi*
2. Open a Comedi device and prepare an insnlist or single insn with write opcode and n < MIN_SAMPLES
3. Invoke the ioctl so that the handler reads the uninitialized tail of the data buffer
4. Extract leaked kernel memory from the returned data buffer
5. Use disclosed bytes to defeat KASLR or locate credentials for further escalation

How to detect it

Review kernel audit logs and dmesg for unusual Comedi ioctl activity; inspect user-space processes issuing comedi instructions that write fewer than 16 samples; search process memory dumps or strace output for ioctl calls with COMEDI_INSN or COMEDI_INSNLIST on Comedi file descriptors.

What your security team should do

• Prioritize kernel updates on all systems exposing Comedi interfaces within the next 30 days
• Restrict Comedi device access via udev rules or DAC to only trusted processes
• Monitor EPSS trend and threat actor activity for similar kernel memory disclosure CVEs
• Audit custom Comedi subdevice handlers for out-of-bounds reads on instruction data