# CVE-2016-7777: Race condition in n/a

> Local guest users can read or modify FPU/MMX/XMM registers of other tasks by exploiting a race condition during instruction emulation.

- **Severity:** Medium 6.3 (`CVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/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:** 7 Oct 2016
- **Updated:** 6 Aug 2024
- **Also known as:** ALPINE-CVE-2016-7777, DEBIAN-CVE-2016-7777, DLA-699-1, GHSA-cr4c-368c-2fc2, UBUNTU-CVE-2016-7777

## What is CVE-2016-7777?

CVE-2016-7777 is a medium-severity vulnerability in Xen Xen, published on 7 Oct 2016. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Xen 4.7.x and earlier does not properly honor CR0.TS and CR0.EM, which allows local x86 HVM guest OS users to read or modify FPU, MMX, or XMM register state information belonging to arbitrary tasks on the guest by modifying an instruction while the hypervisor is preparing to emulate it.

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2016-7777?

It affects 1 product.


Products: Xen Xen.

## How do I fix CVE-2016-7777?

Apply the vendor's patch.

## Is CVE-2016-7777 being exploited?

There is no known exploitation of CVE-2016-7777 in the wild and no public exploit code.

## Other vulnerabilities in Xen Xen

- [CVE-2017-10912](https://insights.sbomify.com/CVE-2017-10912/): Privilege escalation in n/a (critical 10.0)
- [CVE-2017-10918](https://insights.sbomify.com/CVE-2017-10918/): Memory corruption in n/a (critical 10.0)
- [CVE-2017-10920](https://insights.sbomify.com/CVE-2017-10920/): Memory corruption in n/a (critical 10.0)
- [CVE-2017-10921](https://insights.sbomify.com/CVE-2017-10921/): Memory corruption in n/a (critical 10.0)
- [CVE-2025-27466](https://insights.sbomify.com/CVE-2025-27466/): Mutiple vulnerabilities in the Viridian interface (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2016-7777 and fix it if it is affected.

What it is: CVE-2016-7777 is a medium-severity vulnerability in Xen Xen, published on 7 Oct 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-2016-7777 in the wild and no public exploit code.

Affected product: Xen Xen. 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-2016-7777/ (Markdown: https://insights.sbomify.com/CVE-2016-7777/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2016-7777
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2016-7777
- OSV: https://osv.dev/vulnerability/CVE-2016-7777

---
From sbomify Insights: https://insights.sbomify.com/CVE-2016-7777/
Summaries are generated and may contain mistakes; the official description above is the record.