# CVE-2026-3842: Qemu-kvm: hyperv/syndbg: missing mapped-length guard after cpu_physical_memory_map causes host oob write

> A local attacker in a guest VM can trigger an out-of-bounds write in QEMU, leading to memory corruption, information disclosure, or denial of service.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Jul 2026
- **Updated:** 1 Sep 2026
- **Also known as:** AZL-92502, BELL-CVE-2026-3842, DEBIAN-CVE-2026-3842, ECHO-334b-1c04-aa69, GHSA-6mwr-p34x-55cv, UBUNTU-CVE-2026-3842

## What is CVE-2026-3842?

CVE-2026-3842 is a high-severity memory corruption vulnerability in Red Hat Enterprise Linux 10, published on 16 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A flaw was found in QEMU. This vulnerability allows a local attacker within a guest virtual machine to write data beyond its allocated memory. This occurs when cpu_physical_memory_map() returns a shorter length than expected, leading to an out-of-bounds write. Successful exploitation could result in unauthorized access to guest memory or corruption of heap-allocated objects, potentially causing information disclosure, data integrity issues, or a denial of service.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-3842?


## How do I fix CVE-2026-3842?

Apply the vendor's patch.

## Is CVE-2026-3842 being exploited?

There is no known exploitation of CVE-2026-3842 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-3842 and fix it if it is affected.

What it is: CVE-2026-3842 is a high-severity memory corruption vulnerability in Red Hat Enterprise Linux 10, published on 16 Jul 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-2026-3842 in the wild and no public exploit code.

Affected product: Red Hat Enterprise Linux 10. 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-2026-3842/ (Markdown: https://insights.sbomify.com/CVE-2026-3842/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-3842
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-3842
- OSV: https://osv.dev/vulnerability/CVE-2026-3842

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-3842/
Summaries are generated and may contain mistakes; the official description above is the record.