# CVE-2026-99156: scsi: st: Fix use-after-free race between st_remove() and st_open()

CVE-2026-99156 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-99156, released November 3, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-99156
- Priority: High
- CVSS: 7.8 (Important)
- EPSS: 0.0013
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 28, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-99156

## Description

In the Linux kernel, the following vulnerability has been resolved:  scsi: st: Fix use-after-free race between st_remove() and st_open()  st_remove() drops the probe reference on the scsi_tape with kref_put() and only afterwards removes its index from st_index_idr. If that was the last reference, scsi_tape_release() frees the structure while it is still published in the idr.  scsi_tape_get(), called from st_open(), looks up the tape in st_index_idr and takes a reference under st_ref_mutex and st_index_lock. remove_cdevs() does not wait for opens that are already past chrdev_open(), so an open that is blocked on st_ref_mutex while st_remove() holds it can take the mutex as soon as st_remove() drops it, find the freed tpnt in the idr and call kref_get() on it:    BUG: KASAN: slab-use-after-free in st_open   Write of size 4 ...    st_open (drivers/scsi/st.c:254 drivers/scsi/st.c:1291)    chrdev_open   ...   Freed by task ...:    kfree    st_remove (drivers/scsi/st.c:4512)  Remove the index from the idr before dropping the reference, all under st_ref_mutex. A concurrent scsi_tape_get() now either runs first and holds a valid reference that keeps the tape alive, or runs afterwards and finds nothing, so st_open() fails with -ENXIO.  This restores the ordering st_remove() had before the conversion to st_index_idr, where the tape was unpublished from scsi_tapes[] before the final kref_put().

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-99156](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99156.md) | Nov 3, 2026 |
| Linux | linux Debian 14 | 7.2.13-1 | [DEBIAN-CVE-2026-99156](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99156.md) | Nov 3, 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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