# CVE-2026-80550: s390/vfio_ccw: Fix out of bounds check on CCW array

CVE-2026-80550 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-80550, released August 27, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-80550
- Priority: High
- CVSS: 7.9 (Moderate)
- EPSS: 0.0014
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Aug 26, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-80550

## Description

In the Linux kernel, the following vulnerability has been resolved:  s390/vfio_ccw: Fix out of bounds check on CCW array  The routine ccwchain_calc_length() counts the number of channel command words (CCWs) that are chained together in a single channel program, and rejects anything larger than CCWCHAIN_LEN_MAX (256) CCWs.  The loop itself is "do..while (count < 257)", and while the logic in is_cpa_within_range() correctly adjusts between the 0-index array of CCWs and the count of CCWs starting at 1, this means it would look at a possible 257th CCW before ending the loop and (correctly) returning an error.  Fix this by restructuring the loop to break as soon as 256 CCWs (thus indexes 0-255) are examined, without looking at memory outside the range.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 6.1.187-1 | [DEBIAN-CVE-2026-80550](https://patchblox.com/security/data/fix/linux/debian-cve-2026-80550.md) | Aug 27, 2026 |
| Linux | linux Debian 13.5 (trixie) | 6.12.105-1 | [DEBIAN-CVE-2026-80550](https://patchblox.com/security/data/fix/linux/debian-cve-2026-80550.md) | Aug 27, 2026 |
| Linux | linux Debian 14 | 7.1.10-1 | [DEBIAN-CVE-2026-80550](https://patchblox.com/security/data/fix/linux/debian-cve-2026-80550.md) | Aug 27, 2026 |
| Linux | linux-6.12 Debian 12.15 (bookworm) | 6.12.107-1~deb12u1 | [DEBIAN-CVE-2026-80550](https://patchblox.com/security/data/fix/linux/debian-cve-2026-80550.md) | Aug 27, 2026 |

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Data as of 2026-11-08T13:06:02Z 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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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