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


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 28 Oct 2026
- **Updated:** 28 Oct 2026
- **Also known as:** AZL-111293, BELL-CVE-2026-99155, DEBIAN-CVE-2026-99155, GHSA-p98p-xmcg-j23c, UBUNTU-CVE-2026-99155

## What is CVE-2026-99155?

CVE-2026-99155 is a vulnerability in Linux, published on 28 Oct 2026. 

### Official 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.

## Which versions are affected by CVE-2026-99155?


## How do I fix CVE-2026-99155?

Upgrade to a fixed version.

## Is CVE-2026-99155 being exploited?

There is no known exploitation of CVE-2026-99155 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-99155 and fix it if it is affected.

What it is: CVE-2026-99155 is a vulnerability in Linux, published on 28 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-99155 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-99155/ (Markdown: https://insights.sbomify.com/CVE-2026-99155/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99155
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99155
- OSV: https://osv.dev/vulnerability/CVE-2026-99155

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-99155/
Summaries are generated and may contain mistakes; the official description above is the record.