# CVE-2020-35217: Cross-Site Request Forgery in Vert.x-Web framework

> Attackers can bypass CSRF protection in Vert.x Web by exploiting flawed token verification logic, allowing unauthorized state-changing requests.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/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:** 20 Jan 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-9q69-g5gc-9fgf

## What is CVE-2020-35217?

CVE-2020-35217 is a high-severity vulnerability in n/a, published on 20 Jan 2021. 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

Vert.x-Web framework v4.0 milestone 1-4 does not perform a correct CSRF verification. Instead of comparing the CSRF token in the request with the CSRF token in the cookie, it compares the CSRF token in the cookie against a CSRF token that is stored in the session. An attacker does not even need to provide a CSRF token in the request because the framework does not consider it. The cookies are automatically sent by the browser and the verification will always succeed, leading to a successful CSRF attack.

Weakness: CWE-352 (Cross-Site Request Forgery)

## Which versions are affected by CVE-2020-35217?

8 open source packages ship an affected version, including io.vertx:vertx-web. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `io.vertx:vertx-web` | Maven | From 4.0.0-milestone1 | 4.0.0-milestone5 |
| `io.vertx:vertx-web` | Maven | From 4.0.0-milestone1 | 4.0.0-milestone5 |
| `io.vertx:vertx-web` | Maven | From 4.0.0-milestone2 | 4.0.0-milestone5 |
| `io.vertx:vertx-web` | Maven | From 4.0.0-milestone2 | 4.0.0-milestone5 |
| `io.vertx:vertx-web` | Maven | From 4.0.0-milestone3 | 4.0.0-milestone5 |
| `io.vertx:vertx-web` | Maven | From 4.0.0-milestone3 | 4.0.0-milestone5 |
| `io.vertx:vertx-web` | Maven | From 4.0.0-milestone4 | 4.0.0-milestone5 |
| `io.vertx:vertx-web` | Maven | From 4.0.0-milestone4 | 4.0.0-milestone5 |

Products: Eclipse Vert.x-Web.

## How do I fix CVE-2020-35217?

Upgrade io.vertx:vertx-web to 4.0.0-milestone5 or later.

## Is CVE-2020-35217 being exploited?

There is no known exploitation of CVE-2020-35217 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2026-1002](https://insights.sbomify.com/CVE-2026-1002/): Eclipse Vert.x Web static handler file access denial (medium 6.9)
- [CVE-2023-24815](https://insights.sbomify.com/CVE-2023-24815/): Disclosure of classpath resources on Windows when mounted on a wildcard route in vertx-web (medium 4.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-35217 and fix it if it is affected.

What it is: CVE-2020-35217 is a high-severity vulnerability in n/a, published on 20 Jan 2021. 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-2020-35217 in the wild and no public exploit code.

Affected packages and fixed versions:
- io.vertx:vertx-web (Maven): affected from 4.0.0-milestone1; fixed in 4.0.0-milestone5
- io.vertx:vertx-web (Maven): affected from 4.0.0-milestone1; fixed in 4.0.0-milestone5
- io.vertx:vertx-web (Maven): affected from 4.0.0-milestone2; fixed in 4.0.0-milestone5
- io.vertx:vertx-web (Maven): affected from 4.0.0-milestone2; fixed in 4.0.0-milestone5
- io.vertx:vertx-web (Maven): affected from 4.0.0-milestone3; fixed in 4.0.0-milestone5
- io.vertx:vertx-web (Maven): affected from 4.0.0-milestone3; fixed in 4.0.0-milestone5
- io.vertx:vertx-web (Maven): affected from 4.0.0-milestone4; fixed in 4.0.0-milestone5
- io.vertx:vertx-web (Maven): affected from 4.0.0-milestone4; fixed in 4.0.0-milestone5

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-2020-35217/ (Markdown: https://insights.sbomify.com/CVE-2020-35217/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-35217
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-35217
- OSV: https://osv.dev/vulnerability/CVE-2020-35217

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-35217/
Summaries are generated and may contain mistakes; the official description above is the record.