Linux Kernel ACPI EC UAF on probe defer
CVE-2026-31426 Published on April 13, 2026
ACPI: EC: clean up handlers on probe failure in acpi_ec_setup()
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
Products Associated with CVE-2026-31426
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Affected Versions
Linux:- Version 03e9a0e05739cf872fee494b06c75c0469704a21 and below 022d1727f33ff90b3e1775125264e3023901952e is affected.
- Version 03e9a0e05739cf872fee494b06c75c0469704a21 and below 9c886e63b69658959633937e3acb7ca8addf7499 is affected.
- Version 03e9a0e05739cf872fee494b06c75c0469704a21 and below 808c0f156f48d5b8ca34088cbbfba8444e606cbc is affected.
- Version 03e9a0e05739cf872fee494b06c75c0469704a21 and below d04c007047c88158141d9bd5eac761cdadd3782c is affected.
- Version 03e9a0e05739cf872fee494b06c75c0469704a21 and below be1a827e15991e874e0d5222d0ea5fdad01960fe is affected.
- Version 03e9a0e05739cf872fee494b06c75c0469704a21 and below f6484cadbcaf26b5844b51bd7307a663dda48ef6 is affected.
- Version 5.7 is affected.
- Before 5.7 is unaffected.
- Version 6.1.168, <= 6.1.* is unaffected.
- Version 6.6.131, <= 6.6.* is unaffected.
- Version 6.12.80, <= 6.12.* is unaffected.
- Version 6.18.21, <= 6.18.* is unaffected.
- Version 6.19.11, <= 6.19.* is unaffected.
- Version 7.0, <= * is unaffected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.