# CVE-2016-4020: Information disclosure in n/a

> Local guest OS administrators can read sensitive host stack memory via uninitialized variables in QEMU's KVM VAPIC implementation.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N`)
- **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:** 25 May 2016
- **Updated:** 6 Aug 2024
- **Also known as:** DEBIAN-CVE-2016-4020, GHSA-vcqr-cc8h-57gj, UBUNTU-CVE-2016-4020

## What is CVE-2016-4020?

CVE-2016-4020 is a medium-severity vulnerability in Canonical Ubuntu Linux, published on 25 May 2016. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

The patch_instruction function in hw/i386/kvmvapic.c in QEMU does not initialize the imm32 variable, which allows local guest OS administrators to obtain sensitive information from host stack memory by accessing the Task Priority Register (TPR).

## Which versions are affected by CVE-2016-4020?

It affects 11 products.


Products: Canonical Ubuntu Linux, Debian Debian Linux, Qemu Qemu, Redhat Enterprise Linux Desktop, Redhat Enterprise Linux Eus, Redhat Enterprise Linux Server, Redhat Enterprise Linux Server Aus, Redhat Enterprise Linux Server Tus, Redhat Enterprise Linux Workstation, Redhat Openstack, Redhat Virtualization.

## How do I fix CVE-2016-4020?

Apply the vendor's patch.

## Is CVE-2016-4020 being exploited?

There is no known exploitation of CVE-2016-4020 in the wild and no public exploit code.

## Other vulnerabilities in Canonical Ubuntu Linux

- [CVE-2020-11651](https://insights.sbomify.com/CVE-2020-11651/): SaltStack Salt Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2020-7247](https://insights.sbomify.com/CVE-2020-7247/): OpenSMTPD Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2019-16928](https://insights.sbomify.com/CVE-2019-16928/): Exim Out-of-bounds Write (critical 9.8, exploited in the wild)
- [CVE-2018-6789](https://insights.sbomify.com/CVE-2018-6789/): Exim Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2015-2590](https://insights.sbomify.com/CVE-2015-2590/): Oracle Java SE and Java SE Embedded Remote Code Execution (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2016-4020 and fix it if it is affected.

What it is: CVE-2016-4020 is a medium-severity vulnerability in Canonical Ubuntu Linux, published on 25 May 2016. 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-2016-4020 in the wild and no public exploit code.

Affected product: Canonical Ubuntu 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-2016-4020/ (Markdown: https://insights.sbomify.com/CVE-2016-4020/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2016-4020
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2016-4020
- OSV: https://osv.dev/vulnerability/CVE-2016-4020

---
From sbomify Insights: https://insights.sbomify.com/CVE-2016-4020/
Summaries are generated and may contain mistakes; the official description above is the record.