# CVE-2021-43856: Stored XSS in non-image uploads in Requarks/wiki

> A malicious user can upload files that execute JavaScript when viewed inline, allowing stored XSS attacks against other users.

- **Severity:** High 8.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N`)
- **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:** No
- **Published:** 27 Dec 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-rhpf-929m-7fm2

## What is CVE-2021-43856?

CVE-2021-43856 is a high-severity cross-site scripting vulnerability in Requarks wiki, published on 27 Dec 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

Wiki.js is a wiki app built on Node.js. Wiki.js 2.5.263 and earlier is vulnerable to stored cross-site scripting through non-image file uploads for file types that can be viewed directly inline in the browser. By creating a malicious file which can execute inline JS when viewed in the browser (e.g. XML files), a malicious Wiki.js user may stage a stored cross-site scripting attack. This allows the attacker to execute malicious JavaScript when the file is viewed directly by other users. The file must be opened directly by the user and will not trigger directly in a normal Wiki.js page. A patch in version 2.5.264 fixes this vulnerability by adding an optional (enabled by default) force download flag to all non-image file types, preventing the file from being viewed inline in the browser. As a workaround, disable file upload for all non-trusted users. --- Thanks to @Haxatron for reporting this vulnerability. Initially reported via https://huntr.dev/bounties/266bff09-00d9-43ca-a4bb-bb540642811f/

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2021-43856?

It affects 1 product.


Products: Requarks Wiki.js.

## How do I fix CVE-2021-43856?

No fix has been published for CVE-2021-43856 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-43856 being exploited?

There is no known exploitation of CVE-2021-43856 in the wild and no public exploit code.

## Other vulnerabilities in Requarks wiki

- [CVE-2025-56643](https://insights.sbomify.com/CVE-2025-56643/): Security feature bypass in n/a (critical 9.1)
- [CVE-2026-44224](https://insights.sbomify.com/CVE-2026-44224/): Wiki.js: Privilege Escalation via Missing Group Validation in users.update (high 8.6)
- [CVE-2020-15236](https://insights.sbomify.com/CVE-2020-15236/): Directory Traversal in Wiki.js (high 8.6)
- [CVE-2021-43855](https://insights.sbomify.com/CVE-2021-43855/): Stored XSS via SVG in Requarks/wiki (high 8.2)
- [CVE-2022-23654](https://insights.sbomify.com/CVE-2022-23654/): Improper write access check in Requarks/wiki (high 8.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-43856 and fix it if it is affected.

What it is: CVE-2021-43856 is a high-severity cross-site scripting vulnerability in Requarks wiki, published on 27 Dec 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-2021-43856 in the wild and no public exploit code.

Affected product: Requarks wiki. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2021-43856/ (Markdown: https://insights.sbomify.com/CVE-2021-43856/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-43856
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-43856
- OSV: https://osv.dev/vulnerability/CVE-2021-43856

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-43856/
Summaries are generated and may contain mistakes; the official description above is the record.