# CVE-2021-43787: XSS via prototype pollution

> A prototype pollution flaw in NodeBB's uploader module allows attackers to inject JavaScript, potentially leading to account takeover.

- **Severity:** Critical 9.0 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 29 Nov 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-wx69-rvg3-x7fc

## What is CVE-2021-43787?

CVE-2021-43787 is a critical cross-site scripting vulnerability in NodeBB, published on 29 Nov 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

Nodebb is an open source Node.js based forum software. In affected versions a prototype pollution vulnerability in the uploader module allowed a malicious user to inject arbitrary data (i.e. javascript) into the DOM, theoretically allowing for an account takeover when used in conjunction with a path traversal vulnerability disclosed at the same time as this report. The vulnerability has been patched as of v1.18.5. Users are advised to upgrade as soon as possible.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation), CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes)

## Which versions are affected by CVE-2021-43787?

2 open source packages ship an affected version, including nodebb. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `nodebb` | npm | From 1.15.0 | 1.18.5 |
| `nodebb` | npm | From 1.15.0 | 1.18.5 |

Products: Nodebb Nodebb.

## How do I fix CVE-2021-43787?

Upgrade nodebb to 1.18.5 or later.

## Is CVE-2021-43787 being exploited?

There is no known exploitation of CVE-2021-43787 in the wild and no public exploit code.

## Other vulnerabilities in NodeBB

- [CVE-2023-26045](https://insights.sbomify.com/CVE-2023-26045/): NodeBB vulnerable to path traversal and code execution via prototype vulnerability (critical 10.0)
- [CVE-2020-15149](https://insights.sbomify.com/CVE-2020-15149/): Account takeover in NodeBB (critical 9.9)
- [CVE-2023-43187](https://insights.sbomify.com/CVE-2023-43187/): Code injection in n/a (critical 9.8)
- [CVE-2021-43786](https://insights.sbomify.com/CVE-2021-43786/): API token verification can be bypassed (critical 9.8)
- [CVE-2022-46164](https://insights.sbomify.com/CVE-2022-46164/): Account takeover via prototype vulnerability (critical 9.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-43787 and fix it if it is affected.

What it is: CVE-2021-43787 is a critical cross-site scripting vulnerability in NodeBB, published on 29 Nov 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-43787 in the wild and no public exploit code.

Affected packages and fixed versions:
- nodebb (npm): affected from 1.15.0; fixed in 1.18.5
- nodebb (npm): affected from 1.15.0; fixed in 1.18.5

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-2021-43787/ (Markdown: https://insights.sbomify.com/CVE-2021-43787/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-43787
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-43787
- OSV: https://osv.dev/vulnerability/CVE-2021-43787

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-43787/
Summaries are generated and may contain mistakes; the official description above is the record.