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CVE-2026-74549
hwmon: (nct6775-core) Prevent access to unsupported weight registers
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem drivers/hwmon. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74549 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-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Sashiko reports: During initialization of the nct6116 chip, the driver sets data->pwm_num to 5. However, it assigns several NCT6106 register arrays (such as NCT6106_REG_WEIGHT_DUTY_STEP, NCT6106_REG_WEIGHT_TEMP_SEL, and NCT6106_REG_WEIGHT_TEMP_*) to data->REG_PWM and data->REG_WEIGHT_TEMP. These arrays only contain 3 elements. In nct6775_update_pwm(), the driver iterates up to data->pwm_num. If data->has_pwm has bits 3 or 4 set (which is structurally possible for nct6116), the loop attempts to read elements at index 3 and 4 from these 3-element arrays. This results in a global out-of-bounds read, which can be caught by KASAN. Furthermore, the driver uses these garbage out-of-bounds values as hardware register addresses for subsequent read and write operations. This leads to invalid hardware register access, potentially causing hardware misconfiguration or system crashes. The underlying problem is that the chip does support up to five fan control channels, but only the first three support weight control. Fix the problem by extending the affected weight register arrays with zeroed fields. The driver uses zeroed register addresses to determine if a register is supported or not, and skips accesses for unsupported registers.
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/hwmon/nct6775-core.c
- What this is
- HARDWARE MONITORINGMAINTAINERS section matched on drivers/hwmon/ · linux-hwmon@vger.kernel.org · Maintained
- Kernel module
- nct6775_core
Check it on the machine
grep -wE 'CONFIG_HWMON|CONFIG_SENSORS_NCT6775_CORE' /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.
lsmod | grep -w nct6775_corePrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookwormMnot built on amd64/cloud-amd64, arm64/cloud-arm64, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le
- trixieMnot built on amd64/cloud-amd64, arm64/cloud-arm64, armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, s390x/s390x
- forky, sidMnot built on amd64/cloud-amd64, arm64/cloud-arm64, armhf/armmp, armhf/armmp-lpae, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, s390x/s390x
- bookworm · linux-6.12Mnot built on amd64/cloud-amd64, arm64/cloud-arm64, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le, ppc64el/powerpc64le-64k
- M
- a module where it is built at all; some flavours do not build it
- Build switches
- CONFIG_HWMON, CONFIG_SENSORS_NCT6775_CORE
- 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
- 2026-08-15 (2 months 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
- 0.13%, higher than 2.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/hwmon
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.4 | 5.10.265 | 0d11b2a10269 |
| 5.4 | 5.15.216 | 4a77f1d72c6d |
| 5.4 | 6.1.183 | 513d847f7a95 |
| 5.4 | 6.6.151 | 25b528816f5d |
| 5.4 | 6.12.103 | 689082a4cb16 |
| 5.4 | 6.18.44 | 1b722740ac5c |
| 5.4 | 7.1.8 | 4ad2972ef0e1 |
| 5.4 | 7.2 | d0b704e569ac |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | 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
- Exploitation requires local access to hwmon sysfs under /sys/class/hwmon/; any read or write of sensor attributes invokes nct6775_update_device() and reaches the vulnerable nct6775_update_pwm() path via the platform Super I/O driver.
- AC:LAttack complexity, low
- On affected NCT6116 systems with PWM channels 4-5 enabled (has_pwm bits 3-4), triggering is reliable by reading or writing any exposed hwmon attribute; no race or special victim state is required beyond standard sysfs access.
- PR:LPrivileges required, low
- Fan and PWM sysfs attributes are created with mode 0644 and the driver performs no capability or permission checks beyond standard file permissions, so any unprivileged local user can trigger the vulnerable update and store paths.
- UI:NUser interaction, none
- No victim interaction is required; the attacker directly reads or writes hwmon sysfs files to invoke nct6775_update_pwm() and associated store handlers without needing another user to perform any action.
- S:UScope, unchanged
- The vulnerability corrupts kernel driver state and on-chip Super I/O fan/thermal registers on the same host; it does not cross a VM, container, or IOMMU security boundary to impact a separate authority.
- C:HConfidentiality impact, high
- Indexing past the three-element NCT6106 weight register arrays causes a global out-of-bounds read in kernel .rodata (KASAN-detectable), and the resulting bogus register addresses drive unintended hardware reads whose values are cached and returned through sysfs.
- I:HIntegrity impact, high
- Out-of-bounds indices supply valid but incorrect Super I/O register addresses (e.g. auto-temperature registers of other PWM channels) to nct6775_write_value() via writable 0644 sysfs stores, enabling cross-channel fan/thermal misconfiguration.
- A:HAvailability impact, high
- Misdirected reads and writes to wrong Super I/O control registers can corrupt active fan/thermal management on industrial/embedded systems with five PWM channels, potentially causing kernel faults, thermal emergency shutdown, or sustained denial of service.