# CVE-2026-72380: xen/pvcalls: bound backend response req_id before indexing rsp[]

> A malicious Xen backend can trigger an out-of-bounds write in the Linux kernel pvcalls frontend, potentially leading to code execution or denial of service.

- **Severity:** High 8.8 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-110423, BELL-CVE-2026-72380, DEBIAN-CVE-2026-72380, GHSA-44h4-v8mw-w74q, UBUNTU-CVE-2026-72380

## What is CVE-2026-72380?

CVE-2026-72380 is a high-severity memory corruption vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

xen/pvcalls: bound backend response req_id before indexing rsp[]

pvcalls_front_event_handler() takes req_id directly from the
backend-supplied ring response and uses it to index the fixed-size
bedata->rsp[] array for a memcpy() and a store, with no range check. A
malicious or buggy backend can set req_id past PVCALLS_NR_RSP_PER_RING
and drive an out-of-bounds write past the bedata allocation.

req_id was also declared int while the wire field rsp->req_id is u32, so
a range check on the signed value alone is insufficient: a backend
req_id of 0xffffffff becomes -1, passes a >= PVCALLS_NR_RSP_PER_RING
test and indexes bedata->rsp[-1]. Declare req_id as u32 so a single
bound covers both ends.

A backend that sends an out-of-range req_id has violated the wire
protocol, so rather than silently dropping the response, log once and
stop trusting the backend: set bedata->disabled. The event handler then
ignores further responses, and the request paths that wait for a
response return -EIO instead of blocking forever. This mirrors the
fatal-error handling xen-netback uses (xenvif_fatal_tx_err()).

The pvcalls frontend currently trusts its backend, so this is not a
classic-Xen security issue, but it matters for hardening PV frontends
against malicious backends (confidential and disaggregated deployments).

## Which versions are affected by CVE-2026-72380?


## How do I fix CVE-2026-72380?

Apply the vendor's patch.

## Is CVE-2026-72380 being exploited?

There is no known exploitation of CVE-2026-72380 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72380 and fix it if it is affected.

What it is: CVE-2026-72380 is a high-severity memory corruption vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-72380 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-2026-72380/ (Markdown: https://insights.sbomify.com/CVE-2026-72380/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72380
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72380
- OSV: https://osv.dev/vulnerability/CVE-2026-72380

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72380/
Summaries are generated and may contain mistakes; the official description above is the record.