# CVE-2018-16843: Denial of service in nginx

> Attackers can cause excessive memory consumption in nginx via HTTP/2 requests, leading to denial of service, requiring the optional HTTP/2 module to be enabled.

- **Severity:** Medium 5.3 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 7 Nov 2018
- **Updated:** 5 Aug 2024
- **Also known as:** ALPINE-CVE-2018-16843, CLEANSTART-2026-YJ21640, DEBIAN-CVE-2018-16843, GHSA-4p62-4q7w-qmcg, UBUNTU-CVE-2018-16843

## What is CVE-2018-16843?

CVE-2018-16843 is a medium-severity denial of service vulnerability in Apple Xcode, published on 7 Nov 2018. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

nginx before versions 1.15.6 and 1.14.1 has a vulnerability in the implementation of HTTP/2 that can allow for excessive memory consumption. This issue affects nginx compiled with the ngx_http_v2_module (not compiled by default) if the 'http2' option of the 'listen' directive is used in a configuration file.

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2018-16843?

It affects 5 products.


Products: Apple Xcode, Canonical Ubuntu Linux, Debian Debian Linux, F5 Nginx, Opensuse Leap.

## How do I fix CVE-2018-16843?

Upgrade to a fixed version.

## Is CVE-2018-16843 being exploited?

There is no known exploitation of CVE-2018-16843 in the wild and no public exploit code.

Public exploit code:

- based on nginx 1.19.5 to fix for CVE-2018-16843, CVE-2018-16844, CVE-2019-9511, CVE-2019-9513, and CVE-2019-9516 (github_poc): https://github.com/flyniu666/ingress-nginx-0.21-1.19.5

## Other vulnerabilities in Apple Xcode

- [CVE-2025-48384](https://insights.sbomify.com/CVE-2025-48384/): Git Link Following (high 8.1, exploited in the wild)
- [CVE-2014-9390](https://insights.sbomify.com/CVE-2014-9390/): JGit Improper Input Validation vulnerability (critical 9.8)
- [CVE-2019-14379](https://insights.sbomify.com/CVE-2019-14379/): Deserialization of untrusted data in FasterXML jackson-databind (critical 9.8)
- [CVE-2018-4164](https://insights.sbomify.com/CVE-2018-4164/): An issue was discovered in certain Apple products. (critical 9.8)
- [CVE-2016-0746](https://insights.sbomify.com/CVE-2016-0746/): Use after free in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2018-16843 and fix it if it is affected.

What it is: CVE-2018-16843 is a medium-severity denial of service vulnerability in Apple Xcode, published on 7 Nov 2018. 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-2018-16843 in the wild and no public exploit code.

Affected product: Apple Xcode. 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-2018-16843/ (Markdown: https://insights.sbomify.com/CVE-2018-16843/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-16843
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-16843
- OSV: https://osv.dev/vulnerability/CVE-2018-16843

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-16843/
Summaries are generated and may contain mistakes; the official description above is the record.