# CVE-2019-18423: Denial of service in n/a

> A malicious guest administrator can crash the Xen hypervisor on ARM systems via a crafted hypercall, causing a denial of service.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/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:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 31 Oct 2019
- **Updated:** 5 Aug 2024
- **Also known as:** ALPINE-CVE-2019-18423, DEBIAN-CVE-2019-18423, GHSA-jvp4-26qw-rfm7, UBUNTU-CVE-2019-18423

## What is CVE-2019-18423?

CVE-2019-18423 is a high-severity denial of service vulnerability in Debian Debian Linux, published on 31 Oct 2019. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

An issue was discovered in Xen through 4.12.x allowing ARM guest OS users to cause a denial of service via a XENMEM_add_to_physmap hypercall. p2m->max_mapped_gfn is used by the functions p2m_resolve_translation_fault() and p2m_get_entry() to sanity check guest physical frame. The rest of the code in the two functions will assume that there is a valid root table and check that with BUG_ON(). The function p2m_get_root_pointer() will ignore the unused top bits of a guest physical frame. This means that the function p2m_set_entry() will alias the frame. However, p2m->max_mapped_gfn will be updated using the original frame. It would be possible to set p2m->max_mapped_gfn high enough to cover a frame that would lead p2m_get_root_pointer() to return NULL in p2m_get_entry() and p2m_resolve_translation_fault(). Additionally, the sanity check on p2m->max_mapped_gfn is off-by-one allowing "highest mapped + 1" to be considered valid. However, p2m_get_root_pointer() will return NULL. The problem could be triggered with a specially crafted hypercall XENMEM_add_to_physmap{, _batch} followed by an access to an address (via hypercall or direct access) that passes the sanity check but cause p2m_get_root_pointer() to return NULL. A malicious guest administrator may cause a hypervisor crash, resulting in a Denial of Service (DoS). Xen version 4.8 and newer are vulnerable. Only Arm systems are vulnerable. x86 systems are not affected.

Weakness: CWE-193 (Off-by-one Error)

## Which versions are affected by CVE-2019-18423?

It affects 3 products.


Products: Debian Debian Linux, Fedoraproject Fedora, Xen Xen.

## How do I fix CVE-2019-18423?

Apply the vendor's patch.

## Is CVE-2019-18423 being exploited?

There is no known exploitation of CVE-2019-18423 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [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-2019-18423 and fix it if it is affected.

What it is: CVE-2019-18423 is a high-severity denial of service vulnerability in Debian Debian Linux, published on 31 Oct 2019. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2019-18423 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-2019-18423/ (Markdown: https://insights.sbomify.com/CVE-2019-18423/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-18423
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-18423
- OSV: https://osv.dev/vulnerability/CVE-2019-18423

---
From sbomify Insights: https://insights.sbomify.com/CVE-2019-18423/
Summaries are generated and may contain mistakes; the official description above is the record.