# CVE-2020-5403: DoS Via Malformed URL with Reactor Netty HTTP Server

> Attackers can cause premature connection closure via malformed URLs in Reactor Netty, leading to denial of service.

- **Severity:** Medium 6.5 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:R/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:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 3 Mar 2020
- **Updated:** 17 Sep 2024
- **Also known as:** GHSA-hp5x-rqf7-43vf

## What is CVE-2020-5403?

CVE-2020-5403 is a medium-severity denial of service vulnerability in Pivotal Reactor Netty, published on 3 Mar 2020. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Reactor Netty HttpServer, versions 0.9.3 and 0.9.4, is exposed to a URISyntaxException that causes the connection to be closed prematurely instead of producing a 400 response.

Weakness: CWE-755 (Improper Handling of Exceptional Conditions), CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2020-5403?

2 open source packages ship an affected version, including io.projectreactor.netty:reactor-netty-http. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `io.projectreactor.netty:reactor-netty-http` | Maven | From 0.9.3 | 0.9.5 |
| `io.projectreactor.netty:reactor-netty-http` | Maven | From 0.9.3 | 0.9.5 |

Products: Broadcom Reactor Netty.

## How do I fix CVE-2020-5403?

Upgrade io.projectreactor.netty:reactor-netty-http to 0.9.5 or later.

## Is CVE-2020-5403 being exploited?

There is no known exploitation of CVE-2020-5403 in the wild and no public exploit code.

## Other vulnerabilities in Pivotal Reactor Netty

- [CVE-2023-34062](https://insights.sbomify.com/CVE-2023-34062/): In Reactor Netty HTTP Server a malicious user can send a request using a specially crafted URL that can lead to a directory traversal attack (high 7.5)
- [CVE-2019-11284](https://insights.sbomify.com/CVE-2019-11284/): Reactor Netty authentication leak in redirects (medium 6.8)
- [CVE-2020-5404](https://insights.sbomify.com/CVE-2020-5404/): Authentication Leak On Redirect With Reactor Netty HttpClient (medium 6.5)
- [CVE-2026-47848](https://insights.sbomify.com/CVE-2026-47848/): Reactor Netty WebSocket Client Leaks Credentials On Redirect (medium 6.1)
- [CVE-2026-47844](https://insights.sbomify.com/CVE-2026-47844/): Reactor Netty HTTP Server Leaks Exception Details (medium 5.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-5403 and fix it if it is affected.

What it is: CVE-2020-5403 is a medium-severity denial of service vulnerability in Pivotal Reactor Netty, published on 3 Mar 2020. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2020-5403 in the wild and no public exploit code.

Affected packages and fixed versions:
- io.projectreactor.netty:reactor-netty-http (Maven): affected from 0.9.3; fixed in 0.9.5
- io.projectreactor.netty:reactor-netty-http (Maven): affected from 0.9.3; fixed in 0.9.5

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-2020-5403/ (Markdown: https://insights.sbomify.com/CVE-2020-5403/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-5403
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-5403
- OSV: https://osv.dev/vulnerability/CVE-2020-5403

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-5403/
Summaries are generated and may contain mistakes; the official description above is the record.