# CVE-2020-7699: Prototype Pollution

> Attackers can achieve arbitrary code execution or denial of service via prototype pollution in express-fileupload when parseNested is enabled.

- **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:** 30 Jul 2020
- **Updated:** 17 Sep 2024
- **Also known as:** GHSA-9wcg-jrwf-8gg7, SNYK-JS-EXPRESSFILEUPLOAD-595969

## What is CVE-2020-7699?

CVE-2020-7699 is a high-severity code injection vulnerability in express-fileupload, published on 30 Jul 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

This affects the package express-fileupload before 1.1.8. If the parseNested option is enabled, sending a corrupt HTTP request can lead to denial of service or arbitrary code execution.

Weakness: CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes)

## Which versions are affected by CVE-2020-7699?

2 open source packages ship an affected version, including express-fileupload. It affects 2 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `express-fileupload` | npm | All versions | 1.1.9 |
| `express-fileupload` | npm | All versions | 1.1.9 |

Products: Express-Fileupload Project Express-Fileupload, Netapp Max Data.

## How do I fix CVE-2020-7699?

Upgrade express-fileupload to 1.1.9 or later.

## Is CVE-2020-7699 being exploited?

There is no known exploitation of CVE-2020-7699 in the wild and no public exploit code.

Public exploit code:

- 针对 CVE-2020-7699 的复现，软件安全原理课程大作业 (github_poc): https://github.com/zodiac12-pub/CVE-2020-7699_reproduce

## Other vulnerabilities in express-fileupload

- [CVE-2022-27140](https://insights.sbomify.com/CVE-2022-27140/): File upload in n/a (critical 9.8)
- [CVE-2022-27261](https://insights.sbomify.com/CVE-2022-27261/): Express-FileUpload Arbitrary File Overwrite (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-7699 and fix it if it is affected.

What it is: CVE-2020-7699 is a high-severity code injection vulnerability in express-fileupload, published on 30 Jul 2020. 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-2020-7699 in the wild and no public exploit code.

Affected packages and fixed versions:
- express-fileupload (npm): affected all versions; fixed in 1.1.9
- express-fileupload (npm): affected all versions; fixed in 1.1.9

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-2020-7699/ (Markdown: https://insights.sbomify.com/CVE-2020-7699/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-7699
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-7699
- OSV: https://osv.dev/vulnerability/CVE-2020-7699

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-7699/
Summaries are generated and may contain mistakes; the official description above is the record.