CVE-2026-63930: Linux Kernel Use-After-Free Vulnerability

CVE-2026-63930 Overview

CVE-2026-63930 is a use-after-free vulnerability in the Linux kernel's Industrial I/O (IIO) subsystem. The flaw resides in the iio_hw_consumer_alloc() function within the hardware consumer buffer code. The error cleanup path err_put_buffers iterates through a linked list of buffers using list_for_each_entry() while calling iio_buffer_put(). When a buffer's reference count reaches zero, the buffer is freed, and the next iteration of the loop dereferences the already-freed memory to obtain the next list entry.

Critical Impact
A local attacker with the ability to trigger the IIO hardware consumer allocation error path can exploit freed kernel memory to cause corruption, denial of service, or potential local privilege escalation.

Affected Products

Linux kernel versions containing the vulnerable iio_hw_consumer_alloc() implementation in the IIO buffer hardware consumer code
Linux distributions shipping the affected drivers/iio/buffer/industrialio-hw-consumer.c code prior to the fix
Systems using Industrial I/O sensor drivers with hardware buffer consumers

Discovery Timeline

2026-07-19 - CVE-2026-63930 published to NVD
2026-07-20 - Last updated in NVD database

Technical Details for CVE-2026-63930

Vulnerability Analysis

The vulnerability affects the Industrial I/O subsystem in the Linux kernel, specifically the hardware consumer buffer allocation logic. The iio_hw_consumer_alloc() function acquires references to multiple IIO buffers and adds them to an internal linked list. If allocation fails partway through, the function jumps to the err_put_buffers cleanup label to release the buffers already acquired.

The cleanup code uses the standard list_for_each_entry() macro. This macro advances iteration by reading buf->head.next at the start of each loop iteration. Inside the loop body, iio_buffer_put() decrements the buffer's reference count. When the count reaches zero, the buffer memory is freed. The subsequent loop iteration then reads the next pointer from the freed buffer structure, resulting in a classic use-after-free condition.

Root Cause

The root cause is unsafe list iteration during element removal. The list_for_each_entry() macro is not designed to handle deletion or freeing of the current entry within the loop body. Any operation that may release the current list node must use the list_for_each_entry_safe() variant, which caches the next pointer before executing the loop body. The upstream fix replaces the unsafe iterator with list_for_each_entry_safe() to preserve the next pointer before iio_buffer_put() can free the current buffer.

Attack Vector

Exploitation requires local access with low privileges. An attacker must trigger the specific error path in iio_hw_consumer_alloc(), which occurs during initialization of hardware consumer IIO devices. Reliable exploitation depends on inducing an allocation failure while multiple buffers are held on the internal list. Successful exploitation could lead to kernel memory corruption, kernel information disclosure, denial of service through kernel panic, or in some scenarios, local privilege escalation. Refer to the upstream fixes such as Kernel Git Commit 6f5ed4f and Kernel Git Commit b71893c for the exact patched code.

Detection Methods for CVE-2026-63930

Indicators of Compromise

Kernel oops or panic messages referencing iio_hw_consumer_alloc or iio_buffer_put in kernel logs
KASAN (Kernel Address Sanitizer) reports flagging use-after-free access in the IIO buffer hardware consumer path
Unexpected process crashes or system instability on hosts using IIO sensor drivers with hardware buffer consumers

Detection Strategies

Audit installed kernel versions across the fleet and compare against the fixed commits published on kernel.org stable branches
Enable KASAN on test and development kernels to detect use-after-free conditions in the IIO subsystem during driver initialization
Correlate kernel log events referencing IIO driver initialization failures with subsequent instability

Monitoring Recommendations

Ingest dmesg and /var/log/kern.log into a centralized log platform and alert on kernel oops, BUG, or KASAN entries
Monitor loading of IIO drivers and hardware consumer modules on production systems where they are unexpected
Track kernel package versions and flag hosts running kernels older than the fixed builds

How to Mitigate CVE-2026-63930

Immediate Actions Required

Upgrade to a Linux kernel version that includes the list_for_each_entry_safe() fix in industrialio-hw-consumer.c
Apply the vendor-supplied kernel update for your Linux distribution as soon as it is available
Restrict local shell and driver-loading privileges on multi-user systems to reduce local attack surface

Patch Information

The fix replaces list_for_each_entry() with list_for_each_entry_safe() in the err_put_buffers cleanup path of iio_hw_consumer_alloc(). The upstream commits are available at Kernel Git Commit 29783e6, Kernel Git Commit 2ff615f, Kernel Git Commit 6f5ed4f, Kernel Git Commit 9319c94, Kernel Git Commit a3763ae, Kernel Git Commit b71893c, Kernel Git Commit d2759d4, and Kernel Git Commit e965627. Apply the patch set that matches your kernel branch.

Workarounds

Blacklist IIO hardware consumer modules on systems that do not require industrial sensor support using /etc/modprobe.d/ rules
Limit user access to the affected devices under /dev/iio:* through strict file permissions and udev rules
Restrict unprivileged user namespace and module autoload capabilities to reduce the ability to reach the vulnerable code path

bash

# Configuration example: verify kernel version and blacklist the module if unused
uname -r
echo "blacklist industrialio-hw-consumer" | sudo tee /etc/modprobe.d/blacklist-iio-hw-consumer.conf
sudo update-initramfs -u