# CVE-2018-12891: Denial of service in n/a

> A malicious multi-vCPU PV guest can cause a host-wide Denial of Service by bypassing preemption checks in Xen hypervisor code paths.

- **Severity:** Medium 6.5 (`CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/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:** 2 Jul 2018
- **Updated:** 5 Aug 2024
- **Also known as:** ALPINE-CVE-2018-12891, DEBIAN-CVE-2018-12891, GHSA-7945-69h3-wr87, UBUNTU-CVE-2018-12891

## What is CVE-2018-12891?

CVE-2018-12891 is a medium-severity denial of service vulnerability in Debian Debian Linux, published on 2 Jul 2018. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

An issue was discovered in Xen through 4.10.x. Certain PV MMU operations may take a long time to process. For that reason Xen explicitly checks for the need to preempt the current vCPU at certain points. A few rarely taken code paths did bypass such checks. By suitably enforcing the conditions through its own page table contents, a malicious guest may cause such bypasses to be used for an unbounded number of iterations. A malicious or buggy PV guest may cause a Denial of Service (DoS) affecting the entire host. Specifically, it may prevent use of a physical CPU for an indeterminate period of time. All Xen versions from 3.4 onwards are vulnerable. Xen versions 3.3 and earlier are vulnerable to an even wider class of attacks, due to them lacking preemption checks altogether in the affected code paths. Only x86 systems are affected. ARM systems are not affected. Only multi-vCPU x86 PV guests can leverage the vulnerability. x86 HVM or PVH guests as well as x86 single-vCPU PV ones cannot leverage the vulnerability.

## Which versions are affected by CVE-2018-12891?

It affects 2 products.


Products: Debian Debian Linux, Xen Xen.

## How do I fix CVE-2018-12891?

Apply the vendor's patch.

## Is CVE-2018-12891 being exploited?

There is no known exploitation of CVE-2018-12891 in the wild and no public exploit code.

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- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2018-12891 and fix it if it is affected.

What it is: CVE-2018-12891 is a medium-severity denial of service vulnerability in Debian Debian Linux, published on 2 Jul 2018. 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-2018-12891 in the wild and no public exploit code.

Affected product: Debian Debian 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-2018-12891/ (Markdown: https://insights.sbomify.com/CVE-2018-12891/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-12891
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-12891
- OSV: https://osv.dev/vulnerability/CVE-2018-12891

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-12891/
Summaries are generated and may contain mistakes; the official description above is the record.