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CVE-2026-89587
ACPI: pfr_update: fix stack buffer overflow in query_capability()
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem drivers/acpi. Debian urgency: not yet assigned.
Debian does not build this code. The per-release build detail is under "Where it lives" below.
What to do, per Debian release
Debian's own status for CVE-2026-89587 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
query_capability() copies four ACPI buffer objects returned by the firmware _DSM into fixed-size u8[16] fields in struct pfru_update_cap_info using memcpy with the firmware-supplied length: memcpy(&cap_hdr->code_type, elements[CAP_CODE_TYPE_IDX].buffer.pointer, elements[CAP_CODE_TYPE_IDX].buffer.length); The same pattern repeats for drv_type, platform_id, and oem_id. If the firmware returns buffer.length > 16 for any of these fields, memcpy writes past the destination array. struct pfru_update_cap_info is stack-allocated in pfru_ioctl(). Confirmed with KASAN on 7.2-rc6: three stack-out-of-bounds reports are generated when a DSM returns 64-byte buffers, with writes reaching 44 bytes past the end of cap_hdr's [64, 156) frame window into adjacent stack redzones. Introduce a helper pointer to out_obj->package.elements and use it to validate each buffer length against its destination field size before copying, returning -EINVAL if the firmware supplies an oversized buffer.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
drivers/acpi/pfr_update.c
- What this is
- ACPIMAINTAINERS section matched on drivers/acpi/ · linux-acpi@vger.kernel.org · Supported
- Kernel module
- none to look for. The file would have gone into pfr_update, and Debian does not compile it into that module, so finding pfr_update in lsmod would say nothing about this CVE.
Check it on the machine
grep -wE 'CONFIG_ACPI|CONFIG_ACPI_PFRUT' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian does not build this code. In 5 releases below, every kernel flavour Debian publishes has the switch off, so the vulnerable file is compiled into no kernel binary Debian ships.
- bookworm, trixie, forky, sid, bookworm · linux-6.12n
- n
- not enabled on any flavour - this release does not build the code
- Build switches
- CONFIG_ACPI, CONFIG_ACPI_PFRUT
- Reads as
- all on means the file is compiled; any one off means it is not.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-11 (37 days ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.14%, higher than 3.2% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/acpi
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.17 | 6.1.188 | d3af83e32756 |
| 5.17 | 6.6.157 | c5a31b4e7e37 |
| 5.17 | 6.12.109 | a2151624b550 |
| 5.17 | 6.18.50 | 6d4ed2fd022b |
| 5.17 | 7.2.4 | 15d2b7f38f95 |
| 5.17 | 7.3 | ced45be0073a |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The overflow is reached only via local ioctl(PFRU_IOC_QUERY_CAP) or write() on /dev/acpi_pfr_updateN (pfru_ioctl/pfru_write → query_capability). No network, Bluetooth, USB, or packet path evaluates this ACPI _DSM copy.
- AC:LAttack complexity, low
- A single ioctl or write deterministically copies firmware-supplied _DSM buffer lengths into 16-byte stack fields; KASAN reproduced 64-byte DSM buffers writing 44 bytes past cap_hdr. No race or attacker-uncontrollable memory layout is required.
- PR:LPrivileges required, low
- The ioctl/write path has no capable() or namespace check; access is only DAC on the misc device. Although pfrut checks uid 0 and devtmpfs defaults to 0600, Intel PFRU servers reasonably grant /dev/acpi_pfr_updateN to a firmware-management account or container, so privileges are Low.
- UI:NUser interaction, none
- The attacker opens the device and issues PFRU_IOC_QUERY_CAP or write() themselves; no separate victim action such as mounting a filesystem or opening a hostile file is required.
- S:UScope, unchanged
- The overflow corrupts the calling task's kernel stack inside the host kernel. This is local privilege escalation within one security authority, not a VM escape, IOMMU bypass, or sandbox breakout.
- C:HConfidentiality impact, high
- Firmware-controlled memcpy overflows four u8[16] stack fields and adjacent frame state (KASAN: 44 bytes past cap_hdr), which per kernel guidance is memory corruption leverageable for arbitrary kernel memory disclosure.
- I:HIntegrity impact, high
- This is a kernel stack buffer overflow of firmware-controlled length and contents into stack-allocated struct pfru_update_cap_info, overwriting saved registers and the return address and enabling control-flow hijacking.
- A:HAvailability impact, high
- The same out-of-bounds stack writes were confirmed by KASAN and can oops, trip the stack protector, or panic the kernel; the ioctl can be repeated to deny availability.