# CVE-2018-20843: Denial of service in n/a

> Attackers can cause denial of service by sending XML with many colons, exhausting resources in the Expat library.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Jun 2019
- **Updated:** 14 Oct 2026
- **Also known as:** ALPINE-CVE-2018-20843, ALSA-2020:4846, CLEANSTART-2026-ZY15804, DEBIAN-CVE-2018-20843, DLA-1839-1, DSA-4472-1, GHSA-hj5j-c8qp-mgmv, MGASA-2019-0274, RHSA-2020:4846, SUSE-SU-2019:1834-1, SUSE-SU-2019:1835-1, UBUNTU-CVE-2018-20843, USN-4040-1, USN-4040-2, openSUSE-SU-2019:1777-1

## What is CVE-2018-20843?

CVE-2018-20843 is a high-severity denial of service vulnerability in Canonical Ubuntu Linux, published on 24 Jun 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In libexpat in Expat before 2.2.7, XML input including XML names that contain a large number of colons could make the XML parser consume a high amount of RAM and CPU resources while processing (enough to be usable for denial-of-service attacks).

Weakness: CWE-611 (Improper Restriction of XML External Entity Reference)

## Which versions are affected by CVE-2018-20843?

It affects 9 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `mingw32-expat` | AlmaLinux:8 | All versions | 2.2.4-5.el8 |
| `mingw64-expat` | AlmaLinux:8 | All versions | 2.2.4-5.el8 |
| `mingw-expat` | Red Hat:enterprise_linux:8::crb | All versions | 0:2.2.4-5.el8 |
| `mingw32-expat` | Red Hat:enterprise_linux:8::crb | All versions | 0:2.2.4-5.el8 |
| `mingw32-expat-debuginfo` | Red Hat:enterprise_linux:8::crb | All versions | 0:2.2.4-5.el8 |
| `mingw64-expat` | Red Hat:enterprise_linux:8::crb | All versions | 0:2.2.4-5.el8 |
| `mingw64-expat-debuginfo` | Red Hat:enterprise_linux:8::crb | All versions | 0:2.2.4-5.el8 |
| `expat` | SUSE:Linux Enterprise Desktop 12 SP4 | All versions | 2.1.0-21.6.1 |
| `expat` | SUSE:Linux Enterprise Module for Basesystem 15 | All versions | 2.2.5-3.3.1 |
| `expat` | SUSE:Linux Enterprise Module for Basesystem 15 SP1 | All versions | 2.2.5-3.3.1 |
| `expat` | SUSE:Linux Enterprise Server 12 SP4 | All versions | 2.1.0-21.6.1 |
| `expat` | SUSE:Linux Enterprise Server for SAP Applications 12 SP4 | All versions | 2.1.0-21.6.1 |
| `expat` | SUSE:Linux Enterprise Software Development Kit 12 SP4 | All versions | 2.1.0-21.6.1 |
| `expat` | openSUSE:Leap 15.0 | All versions | 2.2.5-lp151.3.3.1 |
| `expat` | openSUSE:Leap 15.1 | All versions | 2.2.5-lp151.3.3.1 |

Products: Canonical Ubuntu Linux, Debian Debian Linux, Fedoraproject Fedora, Libexpat Project Libexpat, Opensuse Leap, Oracle Hospitality Res 3700, Oracle Http Server, Oracle Outside in Technology, Tenable Nessus.

## How do I fix CVE-2018-20843?

Upgrade to a fixed version.

## Is CVE-2018-20843 being exploited?

There is no known exploitation of CVE-2018-20843 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-2018-20843 and fix it if it is affected.

What it is: CVE-2018-20843 is a high-severity denial of service vulnerability in Canonical Ubuntu Linux, published on 24 Jun 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2018-20843 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-2018-20843/ (Markdown: https://insights.sbomify.com/CVE-2018-20843/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-20843
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-20843
- OSV: https://osv.dev/vulnerability/CVE-2018-20843

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-20843/
Summaries are generated and may contain mistakes; the official description above is the record.