# CVE-2026-93238: s390/vfio-ap: fix potential use of uninitialized apm_filtered bitmap

CVE-2026-93238 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-93238, released September 24, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-93238
- Priority: Routine
- CVSS: 3.9 (Low)
- EPSS: 0.0021
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 24, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-93238

## Description

In the Linux kernel, the following vulnerability has been resolved:  s390/vfio-ap: fix potential use of uninitialized apm_filtered bitmap  The DECLARE_BITMAP(apm_filtered, AP_DEVICES) macro allocates the bitmap on the stack without zero-initializing it.  In vfio_ap_mdev_hot_plug_cfg(), the vfio_ap_mdev_filter_matrix() function is only called to initialize and populate apm_filtered if either filter_adapters or filter_domains is true. If the hot plug configuration change only adds control domains (meaning filter_cdoms is true, but filter_adapters and filter_domains are both false), vfio_ap_mdev_filter_matrix() is bypassed.  Consequently, apm_filtered is passed to reset_queues_for_apids() with uninitialized stack garbage. This can cause reset_queues_for_apids() to interpret arbitrary stack garbage bits as valid APIDs to reset, potentially performing unintended guest hardware queue resets.  Fix this by zero-initializing the apm_filtered bitmap at the beginning of vfio_ap_mdev_hot_plug_cfg() using bitmap_zero().

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.111-1 | [DEBIAN-CVE-2026-93238](https://patchblox.com/security/data/fix/linux/debian-cve-2026-93238.md) | Sep 24, 2026 |
| Linux | linux Debian 14 | 7.2.6-1 | [DEBIAN-CVE-2026-93238](https://patchblox.com/security/data/fix/linux/debian-cve-2026-93238.md) | Sep 24, 2026 |
| Linux | linux-6.12 Debian 12.15 (bookworm) | 6.12.111-1~deb12u1 | [DEBIAN-CVE-2026-93238](https://patchblox.com/security/data/fix/linux/debian-cve-2026-93238.md) | Sep 24, 2026 |

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Data as of 2026-11-09T01:18:40Z 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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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