# CVE-2020-27782: Denial of service in Undertow

> Attackers can cause a denial of service in Undertow by sending malicious requests with non-RFC compliant characters in query strings.

- **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:** 23 Feb 2021
- **Updated:** 4 Aug 2024
- **Also known as:** DEBIAN-CVE-2020-27782, GHSA-rhcw-wjcm-9h6g, UBUNTU-CVE-2020-27782

## What is CVE-2020-27782?

CVE-2020-27782 is a high-severity denial of service vulnerability in Undertow, published on 23 Feb 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A flaw was found in the Undertow AJP connector. Malicious requests and abrupt connection closes could be triggered by an attacker using query strings with non-RFC compliant characters resulting in a denial of service. The highest threat from this vulnerability is to system availability. This affects Undertow 2.1.5.SP1, 2.0.33.SP2, and 2.2.3.SP1.

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2020-27782?

4 open source packages ship an affected version, including io.undertow:undertow-core. It affects 3 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `io.undertow:undertow-core` | Maven | All versions | 2.0.33 |
| `io.undertow:undertow-core` | Maven | All versions | 2.0.33 |
| `io.undertow:undertow-core` | Maven | From 2.1.0 | 2.1.5 |
| `io.undertow:undertow-core` | Maven | From 2.1.0 | 2.1.5 |

Products: Redhat Jboss Fuse, Redhat Openshift Application Runtimes, Redhat Undertow.

## How do I fix CVE-2020-27782?

Upgrade io.undertow:undertow-core to a fixed version for your release line: 2.0.33 or 2.1.5.

## Is CVE-2020-27782 being exploited?

There is no known exploitation of CVE-2020-27782 in the wild and no public exploit code.

## Other vulnerabilities in Undertow

- [CVE-2020-10718](https://insights.sbomify.com/CVE-2020-10718/): Security feature bypass in Wildfly (high 7.5)
- [CVE-2020-1718](https://insights.sbomify.com/CVE-2020-1718/): Improper Authentication for Keycloak (high 7.1)
- [CVE-2016-1000229](https://insights.sbomify.com/CVE-2016-1000229/): Improper Neutralization of Input During Web Page Generation in swagger-ui (medium 6.1)
- [CVE-2014-8175](https://insights.sbomify.com/CVE-2014-8175/): Auth bypass in n/a (medium 6.0)
- [CVE-2020-10734](https://insights.sbomify.com/CVE-2020-10734/): OIDC Logout redirect in keycloak (low 3.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-27782 and fix it if it is affected.

What it is: CVE-2020-27782 is a high-severity denial of service vulnerability in Undertow, published on 23 Feb 2021. 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-2020-27782 in the wild and no public exploit code.

Affected packages and fixed versions:
- io.undertow:undertow-core (Maven): affected all versions; fixed in 2.0.33
- io.undertow:undertow-core (Maven): affected all versions; fixed in 2.0.33
- io.undertow:undertow-core (Maven): affected from 2.1.0; fixed in 2.1.5
- io.undertow:undertow-core (Maven): affected from 2.1.0; fixed in 2.1.5

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-2020-27782/ (Markdown: https://insights.sbomify.com/CVE-2020-27782/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-27782
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-27782
- OSV: https://osv.dev/vulnerability/CVE-2020-27782

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-27782/
Summaries are generated and may contain mistakes; the official description above is the record.