CVE-2026-23369

Medium · 5.5

CVSS

5.5

EPSS

0.1%

Published

Mar 25, 2026

CISA due date

—

Cloudanix analysis

Schedule a fix SSVC: Track

A timing problem in Linux startup code can make some computers crash when they turn on.

Exploitation: Local Privilege
Attacker needs: Low Privilege
Complexity: Moderate
Impact: Denial Of Service
Component: OS kernel
Class: Race Condition
Remediation: Upgrade
Effort: Medium
Patch risk: Low

What it actually does

Race condition in i801 I2C driver allows concurrent udev threads to trigger deregistration of an ACPI IO handler area; subsequent access to the unregistered area dereferences a NULL lock_ops pointer, causing kernel NULL pointer dereference and panic.

Why it matters to the business

Systems may crash during boot on affected hardware, producing unplanned downtime and requiring manual intervention or reboot cycles until a patched kernel is deployed.

How an attack unfolds

An attacker with local access or a misconfigured boot environment triggers multiple concurrent udev workers that race on ACPI handler registration; the second thread enters the handler after deregistration but before the unregistered check, dereferencing NULL and panicking the kernel.

How to fix it

Update to a Linux kernel containing the revert commit that restores the ACPI lock; apply the latest stable kernel for the distribution that includes this fix.

How to confirm the fix worked

Confirm the revert commit is present in the running kernel source or package changelog; attempt concurrent udev device enumeration on affected hardware and verify no NULL dereference occurs.

Typical attack path

Boot system with i801 hardware and multiple udev threads active
First thread reserves ACPI area and later deregisters it
Second thread enters i801_acpi_io_handler after deregistration
i2c_lock_bus attempts to read lock_ops from now-NULL area
Kernel panics with NULL pointer dereference

How to detect it

Inspect kernel boot logs and dmesg for the exact NULL pointer dereference in i801_acpi_io_handler combined with the backtrace involving acpi_ev_address_space_dispatch and systemd-udevd.

i801_acpi_io_handler+0x2d/0xb0 [i2c_i801]
BUG: kernel NULL pointer dereference, address: 0000000000000000
Oops: 0000 [#1] PREEMPT SMP PTI
CPU:.*PID:.*Comm: systemd-udevd

What your security team should do

Prioritize kernel updates on all systems using i801 I2C hardware
Monitor boot logs for the described NULL pointer backtrace
Test patched kernels in staging environments before broad deployment

The record

In the Linux kernel, the following vulnerability has been resolved: i2c: i801: Revert "i2c: i801: replace acpi_lock with I2C bus lock" This reverts commit f707d6b9e7c18f669adfdb443906d46cfbaaa0c1. Under rare circumstances, multiple udev threads can collect i801 device info on boot and walk i801_acpi_io_handler somewhat concurrently. The first will note the area is reserved by acpi to prevent further touches. This ultimately causes the area to be deregistered. The second will enter i801_acpi_io_handler after the area is unregistered but before a check can be made that the area is unregistered. i2c_lock_bus relies on the now unregistered area containing lock_ops to lock the bus. The end result is a kernel panic on boot with the following backtrace; [ 14.971872] ioatdma 0000:09:00.2: enabling device (0100 -> 0102) [ 14.971873] BUG: kernel NULL pointer dereference, address: 0000000000000000 [ 14.971880] #PF: supervisor read access in kernel mode [ 14.971884] #PF: error_code(0x0000) - not-present page [ 14.971887] PGD 0 P4D 0 [ 14.971894] Oops: 0000 [#1] PREEMPT SMP PTI [ 14.971900] CPU: 5 PID: 956 Comm: systemd-udevd Not tainted 5.14.0-611.5.1.el9_7.x86_64 #1 [ 14.971905] Hardware name: XXXXXXXXXXXXXXXXXXXXXXX BIOS 1.20.10.SV91 01/30/2023 [ 14.971908] RIP: 0010:i801_acpi_io_handler+0x2d/0xb0 [i2c_i801] [ 14.971929] Code: 00 00 49 8b 40 20 41 57 41 56 4d 8b b8 30 04 00 00 49 89 ce 41 55 41 89 d5 41 54 49 89 f4 be 02 00 00 00 55 4c 89 c5 53 89 fb <48> 8b 00 4c 89 c7 e8 18 61 54 e9 80 bd 80 04 00 00 00 75 09 4c 3b [ 14.971933] RSP: 0018:ffffbaa841483838 EFLAGS: 00010282 [ 14.971938] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff9685e01ba568 [ 14.971941] RDX: 0000000000000008 RSI: 0000000000000002 RDI: 0000000000000000 [ 14.971944] RBP: ffff9685ca22f028 R08: ffff9685ca22f028 R09: ffff9685ca22f028 [ 14.971948] R10: 000000000000000b R11: 0000000000000580 R12: 0000000000000580 [ 14.971951] R13: 0000000000000008 R14: ffff9685e01ba568 R15: ffff9685c222f000 [ 14.971954] FS: 00007f8287c0ab40(0000) GS:ffff96a47f940000(0000) knlGS:0000000000000000 [ 14.971959] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 14.971963] CR2: 0000000000000000 CR3: 0000000168090001 CR4: 00000000003706f0 [ 14.971966] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 14.971968] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 14.971972] Call Trace: [ 14.971977] <TASK> [ 14.971981] ? show_trace_log_lvl+0x1c4/0x2df [ 14.971994] ? show_trace_log_lvl+0x1c4/0x2df [ 14.972003] ? acpi_ev_address_space_dispatch+0x16e/0x3c0 [ 14.972014] ? __die_body.cold+0x8/0xd [ 14.972021] ? page_fault_oops+0x132/0x170 [ 14.972028] ? exc_page_fault+0x61/0x150 [ 14.972036] ? asm_exc_page_fault+0x22/0x30 [ 14.972045] ? i801_acpi_io_handler+0x2d/0xb0 [i2c_i801] [ 14.972061] acpi_ev_address_space_dispatch+0x16e/0x3c0 [ 14.972069] ? __pfx_i801_acpi_io_handler+0x10/0x10 [i2c_i801] [ 14.972085] acpi_ex_access_region+0x5b/0xd0 [ 14.972093] acpi_ex_field_datum_io+0x73/0x2e0 [ 14.972100] acpi_ex_read_data_from_field+0x8e/0x230 [ 14.972106] acpi_ex_resolve_node_to_value+0x23d/0x310 [ 14.972114] acpi_ds_evaluate_name_path+0xad/0x110 [ 14.972121] acpi_ds_exec_end_op+0x321/0x510 [ 14.972127] acpi_ps_parse_loop+0xf7/0x680 [ 14.972136] acpi_ps_parse_aml+0x17a/0x3d0 [ 14.972143] acpi_ps_execute_method+0x137/0x270 [ 14.972150] acpi_ns_evaluate+0x1f4/0x2e0 [ 14.972158] acpi_evaluate_object+0x134/0x2f0 [ 14.972164] acpi_evaluate_integer+0x50/0xe0 [ 14.972173] ? vsnprintf+0x24b/0x570 [ 14.972181] acpi_ac_get_state.part.0+0x23/0x70 [ 14.972189] get_ac_property+0x4e/0x60 [ 14.972195] power_supply_show_property+0x90/0x1f0 [ 14.972205] add_prop_uevent+0x29/0x90 [ 14.972213] power_supply_uevent+0x109/0x1d0 [ 14.972222] dev_uevent+0x10e/0x2f0 [ 14.972228] uevent_show+0x8e/0x100 [ 14.972236] dev_attr_show+0x19 ---truncated---

Affected packages

Ecosystem	Package	Introduced	Fixed