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High severity7.0NVD Advisory· Published Apr 13, 2026· Updated Apr 27, 2026

CVE-2026-31426

CVE-2026-31426

Description

In the Linux kernel, the following vulnerability has been resolved:

ACPI: EC: clean up handlers on probe failure in acpi_ec_setup()

When ec_install_handlers() returns -EPROBE_DEFER on reduced-hardware platforms, it has already started the EC and installed the address space handler with the struct acpi_ec pointer as handler context. However, acpi_ec_setup() propagates the error without any cleanup.

The caller acpi_ec_add() then frees the struct acpi_ec for non-boot instances, leaving a dangling handler context in ACPICA.

Any subsequent AML evaluation that accesses an EC OpRegion field dispatches into acpi_ec_space_handler() with the freed pointer, causing a use-after-free:

BUG: KASAN: slab-use-after-free in mutex_lock (kernel/locking/mutex.c:289) Write of size 8 at addr ffff88800721de38 by task init/1 Call Trace: <TASK> mutex_lock (kernel/locking/mutex.c:289) acpi_ec_space_handler (drivers/acpi/ec.c:1362) acpi_ev_address_space_dispatch (drivers/acpi/acpica/evregion.c:293) acpi_ex_access_region (drivers/acpi/acpica/exfldio.c:246) acpi_ex_field_datum_io (drivers/acpi/acpica/exfldio.c:509) acpi_ex_extract_from_field (drivers/acpi/acpica/exfldio.c:700) acpi_ex_read_data_from_field (drivers/acpi/acpica/exfield.c:327) acpi_ex_resolve_node_to_value (drivers/acpi/acpica/exresolv.c:392) </TASK>

Allocated by task 1: acpi_ec_alloc (drivers/acpi/ec.c:1424) acpi_ec_add (drivers/acpi/ec.c:1692)

Freed by task 1: kfree (mm/slub.c:6876) acpi_ec_add (drivers/acpi/ec.c:1751)

The bug triggers on reduced-hardware EC platforms (ec->gpe < 0) when the GPIO IRQ provider defers probing. Once the stale handler exists, any unprivileged sysfs read that causes AML to touch an EC OpRegion (battery, thermal, backlight) exercises the dangling pointer.

Fix this by calling ec_remove_handlers() in the error path of acpi_ec_setup() before clearing first_ec. ec_remove_handlers() checks each EC_FLAGS_* bit before acting, so it is safe to call regardless of how far ec_install_handlers() progressed:

-ENODEV (handler not installed): only calls acpi_ec_stop() -EPROBE_DEFER (handler installed): removes handler, stops EC

AI Insight

LLM-synthesized narrative grounded in this CVE's description and references.

A use-after-free in the Linux kernel's ACPI EC driver occurs when probe deferral leaves a dangling handler, exploitable via unprivileged sysfs reads.

Vulnerability

In the Linux kernel's ACPI Embedded Controller (EC) driver, a use-after-free vulnerability exists in the probe path. When ec_install_handlers() returns -EPROBE_DEFER on reduced-hardware platforms, acpi_ec_setup() propagates the error without cleaning up the already-installed address space handler. This leaves a dangling pointer to a freed struct acpi_ec in ACPICA, leading to a use-after-free when AML accesses an EC OpRegion.

Exploitation

The bug triggers on reduced-hardware EC platforms (ec->gpe < 0) when the GPIO IRQ provider defers probing. Once the stale handler exists, any unprivileged sysfs read that causes AML to touch an EC OpRegion (e.g., battery, thermal, backlight) exercises the dangling pointer. The KASAN report shows a write of size 8 in mutex_lock via acpi_ec_space_handler.

Impact

An attacker with local access can trigger a use-after-free, leading to memory corruption and potential privilege escalation. The vulnerability is rated High with a CVSS v3 score of 7.0.

Mitigation

The fix, committed in multiple stable kernel branches [1][2][3][4], calls ec_remove_handlers() in the error path of acpi_ec_setup() before freeing the EC structure. This ensures the handler is properly removed regardless of how far initialization progressed. Users should apply the latest kernel updates.

References
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AI Insight generated on May 18, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.

Patches

0

No patches discovered yet.

Vulnerability mechanics

AI mechanics synthesis has not run for this CVE yet.

References

6

News mentions

1