CVE-2025-38480 comedi: Fix use of uninitialized data in insn_rw_emulate_bits()
A local attacker can read uninitialized kernel memory or write invalid data to digital output channels via the comedi subsystem.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-38480?
CVE-2025-38480 is a medium-severity vulnerability in Debian Debian Linux, published on 28 Jul 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
comedi: Fix use of uninitialized data in insn_rw_emulate_bits()
For Comedi `INSN_READ` and `INSN_WRITE` instructions on "digital" subdevices (subdevice types `COMEDI_SUBD_DI`, `COMEDI_SUBD_DO`, and `COMEDI_SUBD_DIO`), it is common for the subdevice driver not to have `insn_read` and `insn_write` handler functions, but to have an `insn_bits` handler function for handling Comedi `INSN_BITS` instructions. In that case, the subdevice's `insn_read` and/or `insn_write` function handler pointers are set to point to the `insn_rw_emulate_bits()` function by `__comedi_device_postconfig()`.
For `INSN_WRITE`, `insn_rw_emulate_bits()` currently assumes that the supplied `data[0]` value is a valid copy from user memory. It will at least exist because `do_insnlist_ioctl()` and `do_insn_ioctl()` in "comedi_fops.c" ensure at lease `MIN_SAMPLES` (16) elements are allocated. However, if `insn->n` is 0 (which is allowable for `INSN_READ` and `INSN_WRITE` instructions, then `data[0]` may contain uninitialized data, and certainly contains invalid data, possibly from a different instruction in the array of instructions handled by `do_insnlist_ioctl()`. This will result in an incorrect value being written to the digital output channel (or to the digital input/output channel if configured as an output), and may be reflected in the internal saved state of the channel.
Fix it by returning 0 early if `insn->n` is 0, before reaching the code that accesses `data[0]`. Previously, the function always returned 1 on success, but it is supposed to be the number of data samples actually read or written up to `insn->n`, which is 0 in this case.
Weakness: CWE-908
Which versions are affected by CVE-2025-38480?
It affects 2 products.
Products include Debian Debian Linux, Linux kernel.
How do I fix CVE-2025-38480?
Apply the vendor's patch.
Is CVE-2025-38480 being exploited?
There is no known exploitation of CVE-2025-38480 in the wild and no public exploit code.
Other vulnerabilities in Debian Debian Linux
Sources
Also known as AZL-65898, BELL-CVE-2025-38480, DEBIAN-CVE-2025-38480, GHSA-g4qg-7mgj-p8v6, ROOT-OS-DEBIAN-11-CVE-2025-38480, ROOT-OS-DEBIAN-12-CVE-2025-38480 and 3 more.