# CVE-2018-5733: A malicious client can overflow a reference counter in ISC dhcpd

> A malicious client can overflow a reference counter in ISC DHCP server by sending massive traffic, causing the service to crash.

- **Severity:** Medium 5.9 (`CVSS:3.0/AV:N/AC:H/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:** 16 Jan 2019
- **Updated:** 25 Apr 2025
- **Also known as:** ALPINE-CVE-2018-5733, DEBIAN-CVE-2018-5733, GHSA-6f7q-j62j-5545, UBUNTU-CVE-2018-5733

## What is CVE-2018-5733?

CVE-2018-5733 is a medium-severity vulnerability in Canonical Ubuntu Linux, published on 16 Jan 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A malicious client which is allowed to send very large amounts of traffic (billions of packets) to a DHCP server can eventually overflow a 32-bit reference counter, potentially causing dhcpd to crash. Affects ISC DHCP 4.1.0 -> 4.1-ESV-R15, 4.2.0 -> 4.2.8, 4.3.0 -> 4.3.6, 4.4.0.

Weakness: CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2018-5733?

It affects 8 products.


Products: Canonical Ubuntu Linux, Debian Debian Linux, Isc Dhcp, Redhat Enterprise Linux Desktop, Redhat Enterprise Linux Server, Redhat Enterprise Linux Server Aus, Redhat Enterprise Linux Server Eus, Redhat Enterprise Linux Workstation.

## How do I fix CVE-2018-5733?

Upgrade to a fixed version.

## Is CVE-2018-5733 being exploited?

There is no known exploitation of CVE-2018-5733 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-2018-5733 and fix it if it is affected.

What it is: CVE-2018-5733 is a medium-severity vulnerability in Canonical Ubuntu Linux, published on 16 Jan 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-2018-5733 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-2018-5733/ (Markdown: https://insights.sbomify.com/CVE-2018-5733/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-5733
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-5733
- OSV: https://osv.dev/vulnerability/CVE-2018-5733

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-5733/
Summaries are generated and may contain mistakes; the official description above is the record.