# CVE-2026-80718: mm/percpu-km: fix bitmap overflow and accounting in pcpu_create_chunk()

CVE-2026-80718 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-80718, released August 29, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-80718
- Priority: High
- CVSS: 7.8 (Moderate)
- EPSS: 0.0018
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Aug 28, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-80718

## Description

In the Linux kernel, the following vulnerability has been resolved:  mm/percpu-km: fix bitmap overflow and accounting in pcpu_create_chunk()  In pcpu_create_chunk(), nr_pages is the total contiguous backing allocation, i.e., nr_units * pcpu_unit_pages, but pcpu_chunk_populated() uses it to set chunk->populated, whose size is pcpu_unit_pages, bitmap.  Since bit N in chunk->populated means page offset N inside every unit is backed.  When nr_units > 1, the function writes beyond chunk->populated.  Fix it by using chunk->nr_pages.  It also fixes the global pcpu_nr_empty_pop_pages accounting, since pcpu_balance_free() only iterates up to chunk->nr_pages.  Commit a63d4ac4ab609 ("percpu: make percpu-km set chunk->populated bitmap properly") introduced the bitmap overflow issue.  Later, commit b539b87fed37f ("percpu: implmeent pcpu_nr_empty_pop_pages and chunk->nr_populated") added pcpu_nr_empty_pop_pages and caused the accounting issue.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 6.1.187-1 | [DEBIAN-CVE-2026-80718](https://patchblox.com/security/data/fix/linux/debian-cve-2026-80718.md) | Aug 29, 2026 |
| Linux | linux Debian 13.5 (trixie) | 6.12.105-1 | [DEBIAN-CVE-2026-80718](https://patchblox.com/security/data/fix/linux/debian-cve-2026-80718.md) | Aug 29, 2026 |
| Linux | linux Debian 14 | 7.1.8-1 | [DEBIAN-CVE-2026-80718](https://patchblox.com/security/data/fix/linux/debian-cve-2026-80718.md) | Aug 29, 2026 |
| Linux | linux-6.12 Debian 12.15 (bookworm) | 6.12.107-1~deb12u1 | [DEBIAN-CVE-2026-80718](https://patchblox.com/security/data/fix/linux/debian-cve-2026-80718.md) | Aug 29, 2026 |

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Data as of 2026-11-08T19:12:23Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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