# CVE-2026-99155: scsi: xen/scsifront: Check for a NULL shadow entry on a backend response

CVE-2026-99155 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-99155, released November 3, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-99155
- Priority: Routine
- CVSS: 5.5 (Moderate)
- EPSS: 0.0019
- 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-2026-99155

## Description

In the Linux kernel, the following vulnerability has been resolved:  scsi: xen/scsifront: Check for a NULL shadow entry on a backend response  scsifront_do_response() validates the rqid in a backend response against VSCSIIF_MAX_REQS before using it to index info->shadow[], but then dereferences the entry to test ->inflight without checking that the slot is populated.  Shadow slots are NULL before a command is submitted (the host private area is zeroed at allocation) and are reset to NULL in _scsifront_put_rqid() once a request completes, so an in-range rqid that does not correspond to an outstanding request makes the frontend dereference a NULL pointer.  A malicious or buggy backend can thus crash the guest by returning a response whose rqid is in range but not in flight -- for example a spurious response before any command has been issued, or a duplicate of one already completed.  The ring has only VSCSIIF_MAX_REQS (16) slots, so before the first command every in-range rqid selects a NULL slot.  Reject a response whose shadow slot is not populated.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-99155](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99155.md) | Nov 3, 2026 |
| Linux | linux Debian 14 | 7.2.13-1 | [DEBIAN-CVE-2026-99155](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99155.md) | Nov 3, 2026 |

---

Data as of 2026-11-08T06:59:42Z 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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

Free to use with attribution: show "Data: Patchblox Patch Radar" with a link to https://patchblox.com/security/patch-radar. Terms, including what needs a written agreement: https://patchblox.com/security/patch-radar/use-the-data

Product names, logos and trademarks shown on Patch Radar belong to their respective owners. They are used only to identify the software each security fix applies to and to help readers find their platform. Their use does not imply any affiliation with, or endorsement by, those owners, and Patchblox is not affiliated with any of them.